You can expect a lively debate when GPIs get mentioned...
Most people would say you don't really need one on a 2V Monster as you get used to riding the wide spread of torque rather than chopping up and down the gearbox all the time.
Do you regularly find yourself trying to change up when you're pootling along in 6th gear?
or would noting the revs when you do a few times cure you of the habit?
It could be argued that it ought to be included, given the complexity of the dash/electronics, personally I've only found a GPI useful on track whilst chasing every last bit of performance.
Another healtech product recently got the thumbs up on here
http://ukmonster.co.uk/monster/showthread.php?t=58505