Cock Rings - Have they any effect in sessions?

Do you think cock rings (either penis alone or penis + testicles) have any effect on your sessions?

IMHO, like many supplemental stimulation devices, cock rings may have positive or negative effects on one's personal Anerosessions. The effect of stretching out the scrotal sac can make the skin more sensitive to stimulation and thus add to ones arousal or it could be a distraction, individual variability governs here.

I'm overweight ... and sometimes I feel like this could have an effect on how aneros can work (or not) properly? I don't know, not hitting the prostate properly, or not anchoring properly in the perineum, etc?

While excess fat deposits may have a slight dampening effect on P-tab stimulation I doubt there are corresponding fat layers surrounding your prostate to interfere with this aspect of stimulation.

My libido is very low which doesn't help and I've had frequently HFWO during sessions - maybe a consequence of my premature ejaculation. Nipples have a big effect on me (only started after using aneros) but they generally end up giving me a HFWO)

Cock rings in and of themselves are not going to help with your libido status, that has more to do with your hormonal system, emotional and psychological state. Worrying about premature ejaculation can certainly suppress arousal which in turn will affect your ability to generate Super-O's. The good news here is that you are still orgasmic just not in the manner you'd like, but you can do things to alter your future responses.

I have big balls and when I try to use a penis+balls cock ring I find that either it is not able to hold the balls (they slip off it) or that eventually later they will find a way to do it. My testicles retreat very deep into my body in some situations at which point they are almost like internal organs.

The problem here has to do with the flexibility/stretch of the restraining cock ring. If the material stretches enough to get you testicles IN then it also stretches enough to let them OUT. The solution is to employ a rigid ring which will not allow the testicles to pass through. This may be accomplished with the use of non-stretching cock rings or testicle cuffs.

Like I said I'm overweight so I have fat around the area and the scrotum skin simply transitions to normal skin at some point... if I lose weight (significantly) will the testicles get more "loose" or "well defined" or will they always be this way and it's just my normal anatomy?

Yes, losing weight will loosen things up as the skin which was previously stretched out by the layer of fat will now be relieved of the internal pressure and hang more loosely. It may only be slight but it should be noticeable. Additionally, you can proactively stretch and expand the scrotal sac skin by using ball stretchers which can also act as testicle cuffs. You can also induce your scrotal sac to loosen up by the application of mild heat. Applying heat coaxes the cremaster muscles to relax and allow the testicles to drop in an effort to regulate temperature for optimal sperm production. This is a body hack you can use to your advantage when installing and using testicle cuffs/ball stretchers.

I have premature ejaculation and trying to keep my balls far from the body is a strategy but it is not very easy for me.

Resticting the action of the cremaster muscles from pulling the testicles up close to the body as you near orgasm has been effective for many men in reducing or stopping the onset of the ejaculatory reflex thus allowing for longer pleasure enjoyment and increased arousal buildup to a more intense orgasm later, perhaps even a Super-O. I think it is certainly a strategy worth trying.

With all cock rings, eventually when my balls start retreating it starts to hurt me, in the skin around the grip.

There is a pain/pleasure dichotomy with many forms of genital stimulation. Some initial discomfort from new devices/techniques often will dissipate as we become enured to the experience. You may have already experienced this getting used to the P=tab of your Aneros model, similarly, you will probably get used to a rigid testicle cuff/cock ring. However, if the device is not properly fitted and/or sized, then pain is a distinct possibility and the device should be removed. It is best to be safe and make sure you maintain good blood flow to your genital equipment and any real pain or numbness needs to be rectified immediately by device removal, always play safe! I think employing a ring with well rounded surfaces will minimize discomfort as your cremaster muscles alternately relax/contract your testicles during an Anerosession. Also, keeping your testicles warm will retard their tendency to retreat back up into the body. Good Vibes to You !

Here is my very personal response to the first question:

I use 1 centimeter thick coton rope to tie my balls. I am thin. I have smallish balls, and a very small scrotum (except when flaccid in 90+ degree weather). I use the first technique described in the following video, usually before I am hard so before my balls try to hide inside me:

https://youtu.be/8s8GKAzbySQ

it is impossible for me to do the second technique, « ball isolation » because of the small size of my scrotum. I like Using rope because I can immediately loosen the knot when I am done, I can control tightness, and depending on how I wrap it, I can control the distance I hold my balls from my body (never very far though). And the rope cost me a euro.

Doing this for 5-10 minute periods (I personally wouldn’t do more for fear of hurting something) gets me really going during toy-in sessions, as does tugging my balls. It sets off orgasms right away, and often puts me in a very horny state. But I have ultra sensitive balls in general, to the point where having my balls rubbed by a (talented) partner is one of my (many) favorite sexual acts.

For me ball play treads on a fine line between pleasure and extreme pain, so it is physically and mentally very stimulating. I also have a really strange connection between my balls and my neck/chest, where ball stimulation makes that area of my body very warm and sensitive.

I don’t know if any of this helps, but as you can see, yes, ball play for me (positively) effects my sessions.

I have added a cock ring to my sessions recently and very much enjoy the feeling I get from it. I don't do any sort of wrapping but use a rubber style ring that can be stretched out quite a bit so there is no fear of getting it stuck in place. I usually wait until well into the session and when I get a random hard on I put on the cock ring. Love the sensation and highly recommend it. Also use it during sex with the wife

Thank you for your feedback.

@rumel I'm definitively interested in ball stretching as my testicles right now as you can see in the pictures are not well "separated" from the body at all even when the scrotum is fully soft. When they retract they go really deep to my body to the point it's basically impossible to pick them again. I'm now checking how to get the correct measurement in order to get a steel ring as it's not easy at all for me to make this measurement.

I'm now checking how to get the correct measurement in order to get a steel ring as it's not easy at all for me to make this measurement.

As a word of caution, I would advise that you purchase two piece steel rings so you can be sure you have the ability to remove them easily. The testicles tend to swell due to blood engorged excitement/arousal, this can make removing a one piece steel ring painful or even impossible until the swelling completely abates.
Good Vibes to You !