I bought a beautiful fireplace a few years ago that uses the gel cans. The quality of it is great and I love the fact that it's so portable. I've moved it around to almost every room in my house. The gel flame lasts about 4 hours and it's fine right up until that last 30 minutes. At that time, it does start giving off a bit of an odor. Not too bad, just sort of a tangy smell to it. As for using it as a heating source, you really need to be sitting right in front of it to feel any effects. I don't think it ever warmed up the room that we had it in.
I recently purchased one of the newer electric heat fireplaces and I love it. Again, it's portable and there's no smell. You can even have just the "flame" on without the heat.
Tammi