..came back to look and see if I had reviewed the 8bitdo M30 (I had) as well as to update a couple things.
I purchased a Retro-bit 8-button arcade pad, which looks/feels like a standard 6-button sega controller but comes with two shoulder buttons. Played great for a time, but then the d-pad snapped. Retro-bit did send me the parts to fix it - but shortly thereafter it started to breakdown in other ways.
The M30 2.4 also stopped being recognized by Windows. The weirdest thing, and best I could tell it has something to do with the USB charging cable and/or something on the PCB.
I bought another M30 recently - opting this time for the bluetooth model. I tore the other one apart and realized that the rubber pads inside were identical to the sega originals.
Long story long - 8bitdo must make replacement pads, so had a look on their site. They are not listed specifically, but they do sell conductive pads for their SNES controller. Found something even better IMO...
8bitdo sells mod kits for your original SEGA/SATURN/NES/SNES/PS1 controllers (apparently since 2019) that will make them rechargeable bluetooth controllers. Not only that, but because they will require USB charging - they can also function as USB controllers. For $25 it seems like a pretty small investment.