I know or have researched some of these, some more in depth than others - I'll just make a few comments where I'm somewhat familiar with the design or program.
Geschwender- hy-vo chain design, out of production. Also I find it difficult to trust a chain.
Probably the best designed and most robust drive out there - too bad retirement pretty much put the business out to pasture. Silent chain drives are probably the toughest and least prone to failure out there but they do have very specific design requirements which when not met properly could lead to short chain lives. But then this holds true for gears also.
The chain selection must be made specific to the design condition since these components do have limitations on surface speeds. In my work though I've found fine pitch chains that can handle even a Mazda's 6,000 rpm plus environment quite well so choice is not a limiting factor here.
EPI- their first design failed in service. maybe the redesign will work as planned.
At first glance this seems a very professionally built product. However, reading the myriads of pages at the web site, little details start coming out, details that seem to reveal that the author may not be as familiar with his subject matter as the prolific wordiness might suggest. The best example of this is the discussion of torsional vibration, where certain statements and omissions suggest that the author may not necessarily understand the problem.
Cam- drive- I have no idea what happened with this organization.
Another good company gone due to retirement. I met the owner/engineer some years back and was very impressed with his understanding of the flight issues and his engineering approach. This was a very good product - too bad no-one seems to be willing to pick it up and run with it.
Precision aero- suitability and availability of unit unknown
Wasn't this the belt drive that was developed and produced here in Washington State? Although I didn't like some of the details, the overall product was well made and with a bit of refinement, could have been a real contender in the market. First the company was producing redrive and engine packages and then later, just the redrives. But yes, eventually I think it just folded up - I haven't heard from the owner in years.
Bud Warren- I get the impression that these are automotive components being used for the clutch drive. No known engineering analysis, seems risky to me.
Don't have any first hand experience with this one however, looking at the cases he designs, I'd say that he does not take any account of the flight loads developed by the prop and thus provides no reasonable load paths for those loads to smoothly get resolved in the engine case or engine mount. The Subaru case is downright awful - the drive mechanism looks OK but I wouldn't fly behind it. The V-8 housing does not seem any better.
Vesta- I will have to see what they have available.
Another redrive that is simply inadequate for properly handling the flight loads. Here though it seems like they might have an idea of the problem so they made all the components out of a massive plate so some stability is possible. But personally, I'd still consider this to be a poor design.