This p3 integrated digital gauge works through the diagnostic port and while it looks very nice it is ultimately very expensive for what it is and the accuracy should be questioned. Many of the readings are a calculated guess made up from readings of a number of sensors on the car, simply not comparable to a proper dedicated mechanical gauge set.
People want to see boost because it's constantly changing and looks cool, ok I get that but really your important readings on a tuned forced induction car are oil temp, oil pressure and I'd probably argue that the most important of all would be your fuelling through a wideband AFR gauge with a dedicated wideband lambda fitted into the downpipe.
If you want a much cheaper way of replicating what you get with the p3 integrated gauge set then get yourself a bluetooth OBD2 dongle and buy the Torque app for your Androud phone or tablet and a suitable removable dash/windscreen mount, this sill display everything and a lot more that the P3 one does, the gauges are fully customisable and the dongle costs about £10, the app about £5 and then ideally a 7" tablet if you have one, I use my Google Nexus 7 and it's ideal.
Another nice option is the Depo Racing Multi Gauge which gives you mechanical boost, true oil temp, oil pressure and voltage all in the one gauge. I think it comes with all the specific sensors you need (for the oil temp and pressure) and this could be adapted for any car I'm sure.
