Unfortunately, most of the premium boutique options I have tested actually ignore the basic physics of the M10 ergonomics. I spent way too much on a few of those high-end brass pieces and was pretty disappointed to find they put unnecessary torque on the hot shoe leaf springs. If the tolerances are even slightly off, we are talking microns here, you end up with a wobbly lever that feels gross and can actually mess with your flash sync pins over time. Its a shame because they look nice but the functional design is often lacking in real world use. I eventually gave up on the heavy brass stuff and tried the Haoge THB-M10B Metal Thumb Rest for Leica M10. It is CNC machined from 6061-T6 aluminum, so its lighter and doesnt throw off the cameras center of gravity as much as the brass ones do. What I like specifically is the clearance around the rear dial. Some grips have this massive overhang that makes it impossible to spin the wheel with your thumb if youre wearing thin gloves, but this one is cut thinner right at the pivot point. It gives you the leverage you need for one-handed street shooting without sacrificing access to the actual controls. Just be careful with the silicone padding on the underside; I noticed some units have glue that can get gummy in the heat, so just keep an eye on that. You definitely want something that stays snug without you having to force it into the shoe.

Checking back in on this thread... honestly, I have tried just about every accessory under the sun for the M series over the last decade. While those boutique brass pieces look cool, I found that they dont actually help that much if your palms are sweaty or if its cold out. In my experience, the best way to keep that M10 from sliding around without spending a fortune is to rethink the whole setup:

• Look into the IDS Works Modular Grip for Leica M10 because it gives you a real handle without the bulk.
• If you are dead set on a thumb rest, look for the Haoge THB-M10B Thumb Grip for Leica M10 as it has the best clearance for the dial. Quick tip: if any grip feels loose in the hot shoe, a tiny sliver of electrical tape on the bottom of the grip foot will tighten it right up and protect the finish. Honestly, once you get a solid front grip, the thumb rest becomes less about holding the camera and more about just having a place to park your thumb. Its a total game changer for street shooting. Stick with it tho, the M10 is a beast once you find the right setup.

Yo, congrats on the M10. Its a beautiful machine but yeah, holding that thing without a grip is basically like trying to hold a wet bar of soap after a while. I went through the same dilemma when I got mine and honestly you might want to consider the middle ground before dropping two bills on the official one. I tried the Haoge THB-M10B Metal Thumb Grip for Leica M10 first because I couldnt justify the Leica price tag. Its solid metal and sits pretty flush, but you gotta be careful because some of these cheaper third-party grips can actually put weird stress on the hot shoe if they arent machined perfectly. If you go too cheap, like those generic $15 ones, you risk scratching the brass or having it wiggle around which is super annoying when you are trying to focus. I eventually swapped to the Match Technical Thumbs Up EP-MX for Leica M10 and even tho it costs more, the ergonomics are way better for street shooting. It doesn't really block the dial once you get used to the thumb placement, but make sure to check if you prefer the short or long version depending on your hand size. I would suggest looking for a used Match Technical one on a gear forum to save some cash while still getting that better build quality. Just be sure to check the tension screw regularly so it doesnt slip out while you're walking around Chicago... stay safe out there.

Gonna try this over the weekend. Will report back if it works!