I used to have an el-cheapo one. I'm not sure it ever did anything useful. Some dust from the "grit" would stick to the surfaces, causing them to look lighter, and therefore "cleaned". I eventually stopped bothering with it.
One thing you do want to avoid is scratches and nicks in the porcelain insulator "nose". These can develop into conduction paths ("carbon tracks"). Once a conduction path is etched into the porcelain the plug is done for. The more powerful the "cleaner" is (or the more aggressive the grit) the more I'd worry about this. From what I've learned, unless the plug is obviously fouled you're better off leaving it alone. If the engine is running properly the plug should remain serviceable without your assistance until the electrode wears past the limits (our plugs aren't adjustable for "gap"). If you have an obviously fouled plug the first issue is figuring out what problem is causing it. Once you have that issue squared you can scrape the goop out with a soft bit of wood, which won't scratch the insulator. It might be ok and normal engine operation will bring it back into a "normal" state as long as "carbon tracks" haven't already been etched into the porcelain from misfires.
I've read plenty of posts that suggest spirited high-rpm runs are the best "tool" for clearing the plugs and based upon recent experience I'd tend to agree. A few weeks ago I had such a drive -- about 2 hours worth of "spirited" driving. Afterwards I noticed a definite improvement in smoothness, especially at low rpm "stop and go" traffic. This was before taking the car in for the recall, which seemed to improve the low-end even more.