Also a layperson, but while the courts may have ruled against certain details of background check requirements (like whether certain kinds of restraining orders can be used to disqualify someone from buying or possessing guns) they have not ruled against background checks being required for gun sales as a concept. The entire purpose of these kits, whether the manufacturer says so or not, is to bypass background check laws by selling something that technically doesn’t meet the definition of a firearm but can very easily be modified to become one.
Technically it’s only the fifth circuit that’s decided that DV restraining orders don’t prohibit gun ownership so far, and the case is part of the current term for SCOTUS. My guess would be that SCOTUS will overrule the 5th circuit while still leaving the “historical analog” test from last year that was the basis of that decision in place, but that’s just an assumption on my part.