I have Blitz DTT (dual turbo timer) and it has boost pressure display and also peak hold and customizable boost level warning. Refresh rate is fast and i like how it all works. Simple and effective.
About all the simple a/f meters... I got a feeling from reading tt.net that these things are not much more than just blinking lights, and for some usable data you need wideband O2 thing. Very expensive, but accurate.