OK, thanks. I'm expecting the size, apparently it needs double that to unpack too, so you need 4gb free or it won't install, once install is done though it only takes up around 2gb as you say.
The free version with the 14 day trial has crashed a couple of times, the app just seems to reset and it takes you back to the home screen, I just relaunched it. However, it only did this while I was messing around with it, it hasn't happened while navigating.
I think it's a bargain if it serves me for a few years, I was looking at getting a TomTom Europe unit for around £100 but this looks like it's got a lot more functionality and customisation at a third of the cost.