"To me it felt like the stuttering ordered when there was rumble"
Its limited to the chips in the old 4-play series ( non existent in the advanced chips). The older chips released in 2004 were used in the original Bliss-Box design (2007) and replaced around 2019. This is 4-Play vs 4-Play advanced. These old chips did not have dedicated USB hardware in them, as it was not available in avr chips at the time. Same with Raphnet.
The good thing is that both adapters use the same cables drivers and ID, so its just a dirrect swap.
Retro Arch has older configs for the 2.0 firmware, and the newer configs ( found on Bliss-Box's web site) work with 3.0 or the newer chips.
I don’t want to manage / update 10 different versions of RetroArch anymore. - Not with Bliss-Box you wont.
There are still a lot of controllers I can’t find reliable adapters for. - Not with Bliss-Box https://docs.google.com/spreadsheets/d/1oMFpFBTok4IsV2DBt48HlUafx2qMWoTxGjpKMFjfSDM/edit?pli=1&gid=0#gid=0
Some features, like rumble support, don’t reliably work with some of my adapters. - Not with Bliss-Box, may ways to make it work.
Connect SNES controllers --> start a SNES game with RetroArch --> all buttons for players 1 & 2 work perfectly out of the box. - If you use the latest auto configs yes, there is always learning, but for the most part, if done right, it works. Lots of support.