I have an Airbox Aware 5+ and it does what it says on the tin. Does everything I want, airspace warning and nav, plus it's just like looking at a half mil map ('cos it is a half mil map) so there's no confusion. Look at your map, look at the Airbox and they're exactly the same. I'm only a VFR bimbler, don't know what you would need for instrument approaches etc.
I'm sure the more expensive stuff has more bells and whistles but you have to look at whether you're going to use all the extras. I think mine was about £320.