Generally speaking, all of the already assembled regulators like Milwaukee, Aquatek, Azoo, JBL, the ones that Do78521 mentioned and others all come with poor needle valves and/or the regulators do not provide a stable flow.
The exceptions to this rule are the ones by GLA, SuMo. AquariumPlants's electronic, maknwar's, bettatail's, oldpunk's, btimmer's and others that do use a good regulator and a good needle/metering valve. These are the ones that you should try to purchase. Don't go after that cheap stuff. If you don't have enough money, save up and make a one time purchase. Many people go the cheap route first (even me) and then find out that they purchased a problematic piece of equipment. Then they have to spend more money to get a good one.
You will find many people that like these cheaper, ready built regulators and they will argue that they are fine for our use. They aren't for me. These regulators need to be watched regularly and have their drift adjusted. I prefer the Ronco method: "Set it and forget it." This is what I advocate.
I use Victor two stage regulators. These regulators hold their setting and they are made very well. I suggest a good solenoid like a Burkert 6011, Clippard's mouse, Parker has some good solenoids for our use and others. I use Ideal "1" series needle valves. These are hard to beat for the money. Fabco's NV-55 and their NV-55-18 are very good needles valves. Swagelok's low flow metering valves also work well. Some of their medium flow metering valves will work too. Parker also makes some good metering valves. I have chose to build my own, but GLA, maknwar, bettatail, btimmer, oldpunk and others build good ones too.
Some people like to use single stage regulators. Good ones like Victor, Harris, Matheson, Smith, Concoa and others work well. These same companies make two stage regulators too. I've purchased most of my regulators from ebay. When I purchased my two stage regulators, I found that single stage and two stage regulators were about the same price.
Rex Grigg has a regulator build DIY that will give you an idea of how easy it is. I used his DIY to build my own, but I used different equipment and some different fittings than he did.
Rex's regulator build DIY: http://www.rexgrigg.com/regulator.htm
Matt has some good documented regulator builds. he used very good equipment for his builds.
Matt's builds: http://www.barrreport.com/showthread...or-Build-Links