Fabco and Clippard needle valve from: http://www.wcf.com/co2iron/
"Seeing is believing...(pictures to scale, our brass Fabco with white nylon adapters is 2.5" tall)"
I've never tried the Fabco valve, BTW. Below are comments from my experience.
At one time I had AquariumPlants.com's "The Best" (at the time) regulator which had a Clippard needle valve. It never stabilized. I was constantly adjusting it. I had to buy a pH controller for piece of mind. I kept getting up in the middle of the night checking the bubble count. I was afraid the "drifter" was going to kill my Apistos. AP.com no longer sells this regulator.
I know that AP.com and Rex Grigg don't build regulators with Clippard valves anymore. The Clippard valves are not listed on AP.com's site and Rex doesn't carry them either.
I've picked up new 1/8" FPT medium flow Swagelok metering valves in stainless steel and chrome plated brass with Vernier caliber handles for $10 to $12. I've also picked up similar new Parker metering valves at nearly the same price. You set the bubble count with these valves and forget about it.
Swagelok metering valve w/Vernier caliber handle
The Ideal metering valves are excellent too. They stay rock solid. No drift. I like them so well that Ideal chrome plated 9 valves for a few of us. These are my Rolls-Royce valves.
Ideal stainless steel metering valve
You can buy a brass Ideal valve for $65 and it is many times better than a Clippard. It doesn't need a lock nut to hold it steady. Plus, you can mount an 1/8" FPT JBJ bubble counter on the Ideal valve. Try that with a Clippard using a 1/8" MPT x Male #10-32 adapter. I know what happens because of its tiny #10-32 threads.
One of the very best things that you can purchase for a pressurized CO2 set-up is a very good needle/metering valve. It is money well spent, IMO. And, based on my experience, it doesn't have to cost a lot of money.