I don't mean to be overly critical, but the obvious question seems to be: Do most YC startups use Clerky? If they do, it seems like a huge endorsement, maybe the only one you'll ever need. If they don't, that sounds problematic...
Yup, most do! Check out the customers section on our homepage :) For incorporations, we work together with YC to get everyone set up, so pretty much everyone uses us unless they're already incorporated (then Kirsty and YC's lawyers do whatever cleanup they have to). Most companies end up choosing to use us for their seed round documents too (currently in private beta) - we are by far the most popular option for that.
Perfectly reasonable question - that's what I'd ask myself!
Oh, sounds great! In that case, maybe you should consider saying so explicitly in your homepage. I read about YC so recognized some names, but my takeaway conclusion wasn't as strong as "most YC companies use this, good enough".
Anyway, best of luck in your endeavors.