They are more commonally called "key inserts". I won't bother describing them, just look at the link. There are tons of places that sell them. Do a Google search for "keysert" or "keyed thread inserts" and you will find many suppliers.
http://www.newmantools.com/key.htmThe only real drawback to the key type inserts is that they require a larger hole to be drilled. If the hole you are having trouble with is very close to the edge of the part, you may not be able to use them. Also, they require you to have an install tool that is used to hammer the keys in without bending them. Helicoils require special taps, so the tool is kind of a wash to me.
I use key inserts all the time at work. If they are put in properly they are a very good repair. The outside threads on them are not cut as deep as a standard bolt. I have seen guys do a sloppy job putting them in aluminum and when the bolt was torqued it pulled the key insert straight out. Now they had a bigger mess because they have a very oversized hole.
Helicoils have their place and I do use them from time to time. If the housing you are repairing has thin edges, if the bolt you are putting in does not get removed very often or if the bolt does not have to take a great deal of torque, the are just fine.
All things being equal, the key inserts are a better repair. Do a good job installing them and they are hard to beat.
