Boot from SD, nvme OS

I’ve been running the Rockpi 4 with ubuntu 18.04 directly from nvme for some time. Since Armbian seems to be more up to date and develop faster I’m trying Focal and Buster (both current) from sd. Now it seems really hard to get Armbian to boot from nvme so boot from sd seems the solution. What is the actual downside to this? I see quite some posts of people who want to only use nvme. Is having a small cheap SD just for boot such a bad thing?

Before making a choose on OS, are there any big differences between Buster and Focal besides just personal preference? Are packages faster available on any of the two?

Final question, is adding the raxda sources still advisable when running Armbian or doesn’t it add anything useful?