The check valve in any JBJ-style bubble counter is going to fail pretty quickly (do a search for stainless check valve, and the really cheap ones with the arrow *appear* to be the exact same thing as those in the JBJ bc's ...and they all fail *really* fast). And, though many people really like their JBJ-style bc's, the experiences I've had with mine (6 or 8 total), aside from the cv's (all of which have failed in under a year, most in much less than that), are very poor. Maybe it's that the plastic is not designed for decent pressure (I've had a couple crack while using 30-40 psi for Atomic diffusers). Maybe it's that the plastic is especially prone to brittleness with the combination of water and CO2. Maybe it's that screwing the caps down too tightly is too much for the plastic cylinder to handle. Maybe it's a combination of a poor NPT thread angle on the input, or that I have really bad luck with both the included O-ring and (not used in conjunction, but only after O-rings failed to prevent leaks) teflon tape as a substitute (still leaked ...on several attempts). Maybe it's something else, including the possibility that I'm a barely functional moron (entirely possible).
In any case, I firmly believe that they're absolute garbage. Seriously, a waste of cash, regardless of how cheap you can find them. And my recommendation would be to go with an inline glass counter - any type that has no moving parts - and buy a *quality* check valve separately. And, by "quality", I expect you'll have to spend $20 or more (or just plain get lucky) on your check valve of choice. I'd recommend a Swagelok.
SS-2C2-1/3
SS-2C4-1/3
SS-4C-1/3
Substitute "B" for "SS", and "1" for "1/3" for further options, though a 1/3 psi cv is ideal. Check Swagelok.com and Evilbay.