We used to sell these at the head shop I worked for. They work pretty well personally, but I still think the best are the RooR jars with the acid etched seal, glass on glass.
As far as the seal goes... if the tightpac cracks or warps ANYWHERE it will be useless. You're better off getting either Mason jars or RooR jars. The RooR jars can be pricey though, but they have different sizes.
Edit: The RooR jars can be a pain in the ass to open if you push the top down too much because it's glass on glass so it gets kinda stuck. Here's a tip for that, get a Q tip and get some Petroleum jelly like A&D or something and take a little drop of it on the Q tip and rub it in good into the acid etching. This will help out with that whole getting stuck thing. They are also air tight.