am36, don't worry, I'm one of the few of us on here with a manual X3 and I can confirm that my car has hill start assist. I actually find the electronic handbrake quite good in that you can feel when it's going to release (it's a split second after you release the button) so it's not really an issue. If however, you're holding the car on the foot brake, the HSA will hold the car for a few seconds after you take your foot of the pedal - just enough time to get on the throttle and get the car moving.
I had a 2009 previous generation X3 before this one, and the HSA worked in exactly the same way.
My car's a 2013 model year 20d M Sport (built in September) so I'd guess it's pretty much identical to yours.
Hope ths helps, and feel free to ask if you have any more questions.
2012 BMW X3 20d M Sport Manual - Sapphire Black/Black Leather and a 2015 BMW M4 Coupe - 6 MT in Yas Marina Blue with Full Silverstone Leather.