Personally, I now have zero interest in buying a rebreather until I can really put it through it's paces. Ideally I would prefer to do the training on a unit prior to buying it (aka use a rental or borrowed unit). This is very different than my previous position. Previously I felt that a simple "try dive" isn't enough info for an untrained rebreather diver. I actually chose to buy my first rebreather without any try dive at all. The reason being is I knew nothing of rebreathers and the couple of try dives I did prior to training on other units was cool, but I didn't have enough knowledge to make an informed decision. I was lucky and the first rebreather I picked was the perfect one for me, with very few faults in my opinion. Even with 100+ hours of rebreather time, I think a quick 20 minute try dive would only give minimal information. I would much prefer to do a lenghty try dive (which good instructors will allow) or to take the course on a rental unit (which can be hard to do since not many people have rentals).
The reason my opinion has switched is due to the sidewinder. I tried it briefly for about 15 minutes several years ago when it first came out. I really liked it because it trimmed out perfectly immediately. I felt it was awkward to breathe on but I chalked that up to having zero rebreather experience other than those 15 minutes. I've been back and forth about the sidewinder since then because when it first came out so many people said it was a POS with lots of issues. The funny thing is alot of people who claimed it was a POS are now pushing them like crazy (because of a vested interest). I know a few people who dive them (their first rebreathers) that love them and to be honest I bought into the internet hype about how amazing a unit is. I was gung ho on the sidewinder, had no doubts I wanted one, so I set up the course and told the instructor all the add-ons I wanted (such as dil mav and needle valve), and fully planned on leaving the class with a unit. Unfortunately from day 1 I hated pretty much everything about the unit. The only thing I actually really liked about it was it trims you out amazingly well and it's a sidemount rebreather. Other than that, it breathes like crap, it's fiddly to set up, the mavs suck in my opinion, it has what I consider scary flood tolerance, and it's pretty much impossible to not end up with wet sorb. Each day of the class I disliked it even more, and for my diving felt the unit was not safe enough in my hands to be a unit I'd comfortably dive regularly. I left the class without a unit. The instructor was nice enough to just charge me a rental fee equivalent for the unit.
Due to that experience, I would really prefer either a long try dive or more importantly to just take the class without the required commitment to either buy the unit or having had to pre-buy the unit before class. I have an interest in the chest mounted optima, but I won't even consider it unless I can sign up for a class and use a borrowed unit. It does mean you're potentially paying for a class you'll never use or are paying a rental fee, but it's worth it to me. If you pick a good instructor, it will never be a loss in my opinion because you should learn something. Eventhough I hated the sidewinder, the class was still a positive experience and I did learn a few things.
Hope that helps.
One other frustration is that all I heard going into class was how amazing the sidewinder was. Now after class when people with the unit ask me how it went and I explain I wasn't a fan and what I didn't like I get the true negative comments nobody likes to say on the internet. The most common comment I get is an agreeance of how horrible it's flood tolerance is. Of course pre-class when I asked I got "oh it's not as bad as you've heard."
