Here’s one testing input lag between the 8Bitdo m30 Bluetooth, m30 2.4Ghz, and Krkizz Joyzz 6 Button controller. Bluetooth has significantly more lag then the 2.4Ghz receivers so if you want to play on an original console on a CRT then it’s best to avoid the kits and Bluetooth controllers and just get the 2.4Ghz controllers.
Most people who buy the Bluetooth DIY kits or controllers usually want to use them on PC or modern consoles like the switch. Since these consoles already have a pretty high input latency for their own controllers, like the switch joycons or Pro controllers or PS4 Dualshock, it’s not really noticeable since the input latency is comparable.
That being said, I have an 8bitdo Bluetooth retro receiver for the SNES and provided you’re not playing a fast twitchy game, it works fine. I play RPGs like Dragon Quest and Final Fantasy on my CRT and don’t notice any lag since those games are slow menu based affairs.