I guess that CDI module failure is pretty common, but like you say... $12. No big deal. Plus, fixing those little issues should be a good experience. I can teach them how to troubleshoot and repair. Father/son stuff.
Don't get me wrong. There are definitely some corners cut on these things. There's no way I would buy one of the bigger units and go hard core blasting through the desert. But, for putting around the yard, these things are perfect. Especially when you consider 1.) They will outgrow them before they wear out. 2.) I will probably be able to resell them for better than half of what I paid new.