I think any of the decently made thumbrests rock. I have the Lensmate for my X100S, but also had a Match Technical for the X-E1. I preferred the brass construction of the Match Technical release, but the price of the Lensmate. In any case, they really transform the handling of either camera for me.
I have Lensmates on my X-Pro1, X-T1 and X20 (the X100 one fits the latter perfectly). I wouldn't be without them. I had a Match Technical one on my Leica M7 and have been a fan of such things ever since. The cheapo ones on eBay are rubbish; not made to tolerance. I had the devil of a job getting one out of a hotshoe. Buy cheap, buy twice...
I can get by on the X100 sans thumb grip, though I prefer one. Just picked up an X100T. A thumb grip is more important with the T, for me, because of the drive button. The Lensmate option looks good for $60, but this $10 eBay special maybe looks better (in terms of not interfering with controls). http://www.ebay.com/itm/331677971325
I always go by the motto "buy once, buy smart". I went with the Match Technical for my X100T because of it's known quality. Lensmate thumb grips also get raves. Personally, I'd avoid the eBay "specials". As for the Match Technical X100T thumb grip, I can't say enough good things about it. Physical design and quality are top notch.
I totally agree. I have Lensmates on my X100T and one of my X-T1's and really feel like they complete the camera. I recently snapped up a second X-T1 that I found a great deal on, and wow....I'm going to have to order another thumb rest .
The Match Technicals are great, too - I have one of those on my X-Pro1. Mine is in the form of the Fujifilm-branded "X-Pro1 Ergonomic Extension Kit" (thumb rest and soft shutter release bundle) that I found on sale for under USD100. For any X-Pro1 users looking for a thumb rest, this Ergo Extension Kit is actually a Match Technical E-7s simply boxed in a black Fuji box, also including a very nice (not Match Technical, I don't believe, but I'm not sure who makes it) soft shutter release.