The Leica M-TL adapter is $400. It is a very nice piece ($400!) and reads to the camera, either letting the camera know what coded lens is on it, or allowing you to set a lens coding manually. This last bit is important, as even with a 3rd party non coded lens, you can still set a coding for it.
But $400? So my attention was caught by a Chinese adapter on ebay for $15.
I decided that I would sacrifice the $15 in the interests of science, and find out for you my fellow rff'rs, if this would work in any capacity or was truly a piece of poop.
Full disclosure - I do not have a TL mount camera (SL, CL, TL etc) - and at this time I don't think I'd get one (I think my $$ would be better off in my wallet or with a D850 film scanner I mean camera) so I have no dog in this fight. Just some free time to kill in the interest of science.
The good - the adapter is made very well, and fits perfectly on the CL. Nice, tight, no play, perfect. The bad (let's cut to the chase) - no lens coding (obviously), but for me much much worse - you cannot magnify the image in the VF for fine tune focusing. I think our esteemed RFF'r Godfrey mentioned this as a possibility. No matter how much I dug into the menus etc, no matter how much the store reps did, there was nothing there. I took the $15 adapter off, put the $400 Leica one on, and BOOM!, you can magnify the image.
So yup, with the $15 adapter you can only focus in the standard view. Which in my usage actually was fine, most of my pics were in sharp focus even wide open because the image actually is clear AND the focus peaking works really well. Much much better than in the lousy stick on EVF for my M240.
For me, losing the lens coding does not matter as I shoot in RAW and in LR pick whichever lens profile I want to use. Losing magnification I can see being an issue in certain cases but I have a feeling that your hit rate in these circumstances (low light, low contrast) would still be much higher than using an OVF rf like on a regular M.
On to the snaps I took around the store with a CL, a Summilux 50 Asph, and a $15 Chinese adapter: