I had a Mallory 140 pump and a return style regulator on my Cobra when I built it. Had a bit of trouble with the pressure building up at idle. At first, I was using 3/8" lines for return and supply. Then I went to 1/2" return and it worked OK. Rebuilt the regulator (Replaced the diaphrams) 3 times in 2 months. Finally got everything working OK, then got a wild hair, pulled all that crap off and installed a mechanical pump with a 1/2" fuel line and haven't looked back in a year. I personally like the simplicity of a mechanical pump. The less crap (Moving parts) I have to worry with, the better I like it.
Reliable? I'm not sure.