I bought one of these a while ago to see what it was like. If you're in the US it'll be fine, but for euro locks they need some serious modification to fit into the keyways. I tried it in a couple of locks and realised the only one it actually fit snugly into was an old practice lock with an SC1 keyway. I had to taper the prongs in towards each other and file one of them flatter, and even then I had trouble getting it into certain keyways. It fit fairly well by the time I finished with it, but because there was no real feedback and it was a bit fiddly to work with, I gave it away. It would have sat collecting dust otherwise... nothing beats a good old fashioned tension wrench.
If you're gonna buy one of these for any kind of serious use, don't get the basic one. The more expensive ones have a little spring mechanism to push the prongs in towards each other, so you can adjust them to fit different keyways. I imagine you'd still need to make them thinner for euro locks, but I can't say for sure as I haven't actually held one in my hand. If you're working with big open keyways like weiser and kwikset, and you don't mind the diminished feedback, go ahead and treat yourself. If you want it as a serious tool, get the HPC version or one of its clones. They don't call this thing "basic" for nothing.
