The fabco are about the best for $ I'd say, easy to add also to an existing system.

John F. from SF wrote this recently:

I compared the STC CV1/4N1/8 ($6.67), the Clippard MNV-4K2
($11.23+shipping) and the Fabco FC-55 ($27.00 from Dave, by
comparison
a local distributor wanted $37.40 for the same one)

9 turns:
Fabco 0-1.76 SCFM (@80 psi)
STC 0-3 SCFM (@60psi)
Clippard 0-5 SCFM (@100 psi)

Sp the Fabco is 2.8X more sensitive than the Clippard.
The Clippard will get the job done, but skimping on the CO2 is never a wise choice.
The STC is much better and as good as any ADA needle valve. A supply surplus place sells them for peanuts here in CA, but I do not use them.

Regards,
Tom Barr