I fit parking sensor a lot, if you've never had a car fitted with parking sensors then a cheap kit will be fine, if you've had a factory fitted kit in the past then your better off spending more.
The main difference between the kit is in the detection zones, cheap kits usually have 3 defined zones, making it a little harder to judge distance than with a more expensive kit, which typically have 5 - 8 zones.
Cobra branded kits are the best, being Original equipment dealer approved kit for many manufacturers. Laserline, and Gemini comes in a close second, Steelmate kits are not bad either. Cobra now do a small 17mm flush sensor too, a little harder to fit but if done wel looks better than a factory kit
Those invisible strip kits are next to useless on anything but a small car, the strips fall off after a few months, and the detection zone is very limited and they dont like the metal beams that are behind most bumpers. if anyone uses the strip ones make sure the bumper is spotless inside and run 2 strips about 5cm apart that seems to help them a bit.
BTW parking sensors will not cause any problems with the can bus if a quality kit is used, i cant comment on the cheaper kits, but if unsure just use a relay to power the parking sensors.
Hope this helps someone