I just got this an hour ago, so admittedly I'm making some snap judgements here.

Also, keep in mind that my house is old, with old-fashioned cloth insulated wiring. It's what electricians call post and tube (porcelain) style wiring. To add to my difficulties in locating wall studs, is that my walls use lathe and plaster. This is the nasty, rough "spray it on the walls" kind of stucco. If you have seen sprayed on stucco with the texture of lumpy oatmeal, you have the idea. It's thick, maybe 1/2 to 5/8 inch plaster over 1/4 board. I suppose this combination represents a worse case scenario for any stud finder. Here's what I experienced:

One annoyance is that the stud finder has a sharp-edged bottom which really catches on rough stucco. I had to drag it at a slight angle to keep it moving. A smooth rounded base would greatly improve this product. The unit came with a 9V battery. I gave it the "tongue-test", and the battery was very fresh. When I tried to turn the unit on it refused to stay on. It turns out that you must keep the power button depressed for about two seconds for it to latch on. The display lights up quite brightly in green, but the LCD display has fairly poor contrast and a poor viewing angle. The view shown in the photos is fairly accurate but from a angle or looking down from above, it's almost invisible. Just remember you will have to face the unit head on to see a clear display.

I wish I could give a definitive answer to the units effectiveness, but my old-school construction make the results very ambiguous. It indicated that wiring in the walls was at a diagonal rather than vertical or along headers and sills. Old wiring? I could detect studs in some cases but the spacings were erratic. Modern construction employs mostly 16 inch spacings for studs, but I was seeing 18 or 20 inch spacings. Is this because the house was made in the 1890's? I have the impression that this product would work fairly well in a more modern style of construction, but it will have limited use for me here, I'm afraid. I'll try to use the device to give me clues on where to drill or cut, but I suspect that I will have to make small 1/8 inch test holes with my drill and spackle the misses. Tedious, but sure. Sorry, I couldn't give a more definitive review, but if your house has similar old-school construction, I would have to recommend a different product.

Works passably fair. The display needs to be viewed head on, it's not nearly as clear as represented in these pictures, and anything off to an angle appears quite dim. Seems to caution adequately for hidden wires and pipes. Finds wood studs ok, and so far reliably. I've only used it on drywall situations.

Works great, and instructions were simple enough. I watched a video as well but if you're like me and had never used one of these before:
1) place stud finder against the wall before turning on
2) hold down the side button until it beeps and continue holding down while scanning for studs
3) Scan for studs by dragging the finder along the wall slowly and horizontally. When it beeps, you've found it!

This works great. Found what I needed right away and was able to put up the TV wall mount quickly.

Works like its suppose to