Sorry for the late reply.
Reasons I don't like adjustable BOVs:
- More prone to failure or leakage
- Over adjustment causes failure
- In the hands of an amateur it can do more harm than good
- Once you've adjusted it properly, you'll never need the adjustability ever again
Some items are nice to have that are adjustable, and don't cause too many problems. Manual boost controllers are a good example. Them being adjustable is nice, and the pros outweigh the cons.
BOVs on the other hand, usually work just fine out of the box. If it doesn't for some reason, then replacing the spring with another that matches the amount of vacuum your engine produces is the answer. So I prefer Tial's method (swapping springs) to the screw-type preload method other adjustable BOVs use.
Same thing with adjustable FPRs. If you want to run 4 bar, get a 4bar FPR.
This is my opinion.