If you have or are planning on adding a valved (via boost) exhaust system then get a multi tap boost fitting kit along with the gauge and fitting kit. Forge, APR and 42 Draft Designs sell them for around £40 IIRC.
If you know what your doing the fitting is straight forward but if like me your an idiot then its worth letting someone else have a go, it will also need wiring into the fuss box to allow it to light up and dim along with the dimming function of your instrument cluster.
Main alternative is the Defi but its a lot more expensive. My Newsouth one performs perfectly and more then good enough. There's also a few digital around also.