General consensus I've heard is that Cobra radar detectors are basically your typical bargain bin detectors. As such, their performance will vary from poor to average. However, depending your driving habits (or monetary funds!) it may still provide sufficient warning for you.
The best receiver that doesn't cost thousands right now seems to be the Escort Passport 8500. It's approx ~$250 new. The Valentine One comes a close second at $400 (maybe a little less). The Bel 980 is a close third, and is probably a little less than the Escort, maybe around $200.