Not much use to you, Hardy, but the only time I've ever bought one, it was a cheapie. If I remember, it was around £25, and absolutely useless.
As with all power tools/electronics, the cost varies enormously.
Bosch is a good make, but they have them for £30, or £230 according to taste.
The expensive ones are fine if your job entails using them all the time, but not for DIY.
Call me basic, but I've always just used a cordless drill with a 3mm bit, and drilled holes until I found a stud... very simple. A little blob of filler and paint, and the evidence is gone.
Each to his own though. There are several people here on AB who I'm sure who will be able to help. So hold on.................