Ni Hao @fajun_xu or should I say Xu_FaJun? 
Well, a while back I did give some thoughts regarding hands-free setups in a previous forum discussion from someone looking for recommendations for a hands-free thrusting fleshlight. I recommend perusing that thread for some insights.
To answer your questions:
- What tends to fail most is sleeve alignment IMO vs the other things you mentioned especially in long sessions since one’s GG doesn’t exactly have infinite stamina if you know what I mean and it’s easy to get bored during long sessions causing… slips and misalignments… if you know what I mean…
But to be honest tho, that could be a personal matter if you know what I mean… - Body/base IMO is better in regards to keeping things stable, but to be honest I’ve never used desk-mounting before. I think actually this question is a matter of comfort and user preference since not all people engaging with software that uses stroking devices are doing it in the same way given that there’s a rather wide variety of toy types and play configurations that an individual may find comfortable or uncomfortable. I just find base/body mounting more versatile and comfortable vs. being forced to game at desk. Plus, from a market standpoint, there’s a lot of competition for desk mounts since you can simply build that yourself by buying some parts for a stand off Amazon or something and attaching your toy to that. Not many well made toy harnesses tho…
- Yes? I guess? Primarily because there are just too many different designs for toys out there and it’s hard to get them all to work with a singular harness type. TBH, I don’t have an issue with this personally since I’ve found my optimal play arrangement and toy preference set-up, but if a product did provide adjustable guides, it would be quite helpful for user comfort and just simple versatility when working with all the different toy types and user preference.
- Check out the Awesome List of BPlug supported Onaholes with Linear Actuators for what toys to look into. A short list of toy models to consider looking at: The Fleshy, Joyhub Martino and Mars, Lovense Solace and Solace Pro, of course the Handy, and perhaps the Svakom Hannes Neo. If you’re set on going harness, the two major toy forms you probably need to think about are things like the Fleshy/Hannes Neo/Solace/Joyhub Martino/Mars which are just fleshlight-like devices of various sizes with internal strokers and also toys like the Solace Pro and Handy which have offset external strokers which require a different style of alignment. That of course is for those with GG. No comment on the experience of those on the other side of the coin if you know what I mean, but it would be interesting if such an adjustable harness could work with toys built for the opposite arrangement along with GG… Just a thought…
Anyway, hope my thoughts help you in designing your product! It actually looks pretty interesting! Best of luck!
@blackspherefollower Oy blacksphere! Don’t scare away a newbie who just wanted some feedback on an interesting product they’re designing! Find some light in that black void of a heart you have!