I bought a Turbo Transformer from these guys -
www.turbo-transformer.com, although I believe x-ph on this forum is also a supplier.
I connected to 2 sensors like they have shown here -
They have a free app which was my decision for buying it so I could also watch my boost pressure. Oh and not to mention the price. I adjusted mine to +3 PSI , their default setting is +2 psi because anything more did not increase my peak boost.
I also logged my stfrs with a torq app and it seemed +4 PSI was pushing the STFRs in the +20% range, which is still ok (they didn't look pegged). But my peak boost stayed at 22.6 psi - I figured there is no need to push it. I have had mine since a year or so, I am pretty happy with it.