Much as I've been tempted by a HP2 a couple of times and maybe a 950SE............
I've never pulled the trigger for a HP2, despite a few rides on the road and some offroad
Why................dunno really
The thing that put me off with the HP2, was that I thought it was only half done for these reasons
Underwhelmed forks - should have been 50mm for the weight of the bike and a damn sight better quality and fully adjustable on a £12k bike
Lack of BMW prep and initial design, for a dirtbike
a) Standard 12GS airbox with breather that goes straight into the sump

(should have been re-designed and bespoke for the HP2)
b) Standard 12GS engine (with the balancer shaft removed, cheers Mav

), with no re-designed torque curve and power delivery for an offroad bike - hence it spins-out too easily
c) Gearbox - standard 12GS - with no re-design of the gearing ratios for a dirtbike and the major faux-pas - no low 1st gear - it spins out

d) Can-bus and EWS immobiliser.................why

..............on a dirtbike - it should have a loom all specific to the HP2, not a fecking 12GS
e) Airshock - can be good and can be bad
Frame and rear drive are a work of art

......................but the rest was just not thought out by the BMW design team...............in dirt bike terms
Hence the 950SE is a better machine on paper, although I've never ridden one - so can't comment on the rideability
When the G650XChallenge came out it was no contest for the following reasons
a) Price - it was a bargain
b) It was functionally better thought by BMW out as a dirtbike/dualsport
c) It is lighter and more nimble on the trail and is faster than a HP2 in most dirt situations
d) It has the real ability on the road to cover distance ok and there are similar options to the HP2 to convert it into a true dualsport/Adv Tourer
e) It is well put together and well built in the Aprillia factory
f) The suspension from the HP2, suits the lighter XChallenge better
The same could be said for the KTM 690 v 950SE