I've done the usual testing, , tested complete fuel system by blocking up the return pipe, pressure goes upto 6 bar and the non return valve works a treat, holds 6 bar for ages.
Take the block out of the return pipe so the reg is controlling what goes on when the pump stops priming and instantly after the pump stops it goes down to 1.5 bar (from 3), then drops more slowly from there but is almost empty within a minute. I'm sure that's not right and it should be holding at least 2.5 bar of pressure for 30 mins.

Anyone else using SX reg and has a pressure gauge?

The above testing confirms injectors, fuel pipework, fuel filter and non return valve all working perfectly, it is definately the reg (which I bought last year)..