@beezNeez, The progasm is bigger and will move less, or at least feel like it moves less, keeping in mind any of the models only need to move slightly to produce results. The smaller devices will feel like they are moving much more. They all will work so to speak but they have their own personalities if you will. The progasm for me feels fuller and produces outstanding results at times, whereas the smaller devices feel like they are tapping away consistently and feel good but dont always produce the powerful O's for me. But thats just my opinion, others may have different feelings.
It is unfortunate that @BMayfield put together his survey before the appearance of the Aneros silicone models, such as the Helix Syn.
I became interested in the Aneros in October 2011 when a guy on BateWorld told me about it had done for his life. So I investigated and I got as my first Aneros tools the Helix, MGX, and Progasm Classic. They all looked so formidable to me because I didn't know I could insert them into my anus since I had no experience in anal play. But fortunately I started my sessions in early June 2012 with Helix Syn who introduced me to Anerosing through his soft, silicone touch.