Can’t beat the pricing of https://purelymail.com/. I’ve been using them for a couple years now.

Or just get one that has a trackball/touchpad/trackpoint, like https://ultimatehackingkeyboard.com/

Interference. Especially in apartment complexes, the 2.4Ghz band is busy, causing a lot of packet drops and random disconnects.

I’ve been using purelymail.com for quite some time now, am very happy with it.