I've seen clients run through several of these instead of taking my advice and getting a nice Victor regulator and nice needle valve.

You can get a solenoid and add that.
I think I spent about 30-40$ for the reg, one of the best there are(slightly used), 25$ for the nice valve(Aquacave sells a nice valve as does the 1/8" metering valve from several ebay vendors), 25$ for solenoid.

This is a top notch system.

Regards,
Tom Barr