I couldn't find a thread dedicated to L-mount adapters, surprisingly. Does anyone have experience? I ordered a couple adapters directly from Urth for M42-mount and OM-mount lenses. They canceled my order after a week due to warehouse or fulfillment problems. This means I have an opportunity to reconsider before trying again with Urth.
I'm a fan of Rayqual adapters. They strive to make them precisely the right thickness which often makes hard infinity perfectly usable (esp. when adapting M-mount lenses) and their build quality is great. Availability outside of Japan might be a bit limited though. I have some of their adapters for my Sigma fp (L-mount) as well as for my Sony A7CII and Fujifilm X-S10. https://www.rayqual.com/LeicaLA.html https://www.rayqual.com/tokuchyou.html
I have the Leica adapters for M, R and S lenses. They are all very good but also rather expensive.
The S-adapter can also not be stacked which I found infuriating, e.g. I can use my Contax 645 lenses on an S camera (through the C-to-S adapter) but I cannot stack that adapter with the S-to-L adapter.
Besides that I have Kippon adapters for M39, Pentax Screw M42, Minolta MD and Contax G. Also a Fotasy adapter for Canon FD.
I don't recall any issues but truth be told, most of these I also have not used much.
I have the LLL helicoid adapter for M. I also use an LTM lens with M flange on that adapter sometimes. The adapter doesn't quite hit infinity and the first one I ordered was rough in helicoid action but the replacement is smooth. Both had the infinity issue though but otherwise it works well and gives 35mm lenses a nice close focus option.