Making valve "easy" to remove
If you don't want to convert over a copper union to Pex (which would probably require a little pipe sweating), the Pex unions available are pretty cheesy pieces of junk.

Luckily for you, Pex will twist on it's own fitting. I wouldn't suggest doing it very often, but the once or twice you may have to remove that fitting from the check valve for "inspection", you'll be fine.