The worst of these is Bluetooth. I bought a USB dongle with a chipset said to be compatible.(CSR 8510 A10) Then I found it was a knockoff version of the chipset with some weird ass quirks that make it incompatible with the official drivers. To this day it's the one thing I never bothered to try and fix, even though others have succeeded in making the fix. The fix wasn't something I could easily turn into a DKMS module as I have no idea how to do that, and as a result it had to be compile with the kernel manually and I want ready to go diving into kernel and at the same time also trying to work out exactly what the quirks were.

I eventually bought a dongle with a chipset that worked was either not a knockoff or it was a perfect reproduction. It worked flawlessly, and I've bought more since then for PCs with no Bluetooth support.