I tried to install a R1200GS tachy on my HP2E.
Display said '300 km of fuel autonomy' or something like that (which is not possible, max 200 km with a full tank).
I think that other tachys are not aware of the fact that the HP2E or MM tank is only 13 liters and when the tachy has a signal of 'full tank', it considers (in my example) 20 liters present (tank of GS).
So, go for a MM tachy or original, you can sometimes find one on Ebay.
GSMarc from BELGIUM
2014 KTM EXC450 6Days
2008 HP2/MM ABS
2005 HP2E SM Prototype