I ask that same question and then did a little testing of my own. I put a gauge on the camper side of the regulator shown. I had 70 psi going in and 38 psi coming out. Good, until I turned on the sink. It dropped to 28 coming out. Then turned on the bathroom sink and it dropped to 18. Turned on the shower and it dropped to maybe 5 and was not enough water to do anything with. This is probably why so many think it's just a restrictor. So I bought the Watts adjustable, set it to 40 and did the same test. With 70 on the faucet the camper pressure never dropped below 35 with 3 faucets on and all had useable flow. That was enough for me to justify the cost. Mine is 10 years old and has never been rebuilt and works flawless.