Since I have been using radar detectors for years, maybe I can help.
First and foremost, don't expect your radar detector to save your ass in all situations. About 5 years ago you could pretty much rely on them but not anymore. Some highway patrols now use laser guns instead of radars, and whatever detector you buy will be inefficient against that. It will just tell you "You ve been caught!"
One other thing. The VG-2 undetectable thing is bullshit. This is a very ooooolld technology that is not used anymore. In Quebec you are pretty much ok with a VG2 undetectable radar detector (Quebec is too cheap to buy the necessary detection equipement!
), but if you venture in Ontario at high speeds, they will eventually get you anyway (I know, they seized one from me!). It's a good thing Ontario's fine for using a speed control detection device is not too steep, at least it was not when I got caught, about 2 years ago.
Finally, you better buy one of the best radar detector out there, or you will be highly annoyed by false alarms. Cheap ones will buz at each f**ck**g store with automatic doors, city mode or not.
From my own experience, Bel Electronics and the Escort Passport are the best. I suggest you do a google search on "radar detector reviews" and see by yourself. There's a lot of information available on the subject.
If you need any more info, feel free to PM me.