Which one are you asking about? The stuff that is water based and sold on the shelf at HomeDepot? If so, stay away, the stuff gets horrible reviews, I wouldn't consider it at all.
Rustoleum does have a professional line that is worthy of consideration, it is a solvent based epoxy and is priced very attractively, at least on the surface. It contains fillers that compromise the surface strength and solvents that reduce the film build.
I really am a cheap-*** at heart and I was totally on the fence about Epoxy-Coat vs Rustoleum Pro. The Rustoleum looked cheaper overall, however I had to apply the stuff in a short window so time was a big consideration. According to the instructions I would have had to put at least a couple more layers of Rustoleum Pro down to get the same build as Epoxy Coat. EC claims to be no solvent, it crosslinks. EC also advertised ready to park on in 3 day, which turned out to be quite a bit untrue. It took a week before the surface wasn't tacky at all. I ended up parking on cardboard for a few weeks just to avoid hot tire pickup issues.
Looking back at it, I probably would have spent about $350-400 for a Rustoleum setup to equaly the $500 I spent for the EC. I'm certainly glad I went with that kit as it had more than an adequate amount for a two car garage. I was a bit miffed about their claim that it would be ready to park on so soon, but I'm sure everyone would flock to a competitor if they were completely honest.
The key to using any of the systems is prep work. The prep easily take 2-5x the time that coating the floor does. I started with virgin concrete and prep was still a TON of work. The included acid was a joke, luckily I spent the better part of 16 hours reading garage journal stories on what it really takes to prep the floor.
I think the vendors hold back the truth as if people really knew what is involved in getting a solid bond, they'd just not do it or call a pro.
In all, I'm extremely pleased with the result. My floor is glossier than a most cars. Everyone that sees it can't stop talking about it. There is almost no dust in the garage now. I can't imagine being without it.
If you only take away one bit of advice, this should be it... go to garage journal... read, read, and read some more:
Flooring - The Garage Journal Board
Quick Epoxy-Coat review - The Garage Journal Board <--my review of EC
Epoxy Coat Garage Floor Coating | COMPARATIVE ANALYSIS <--cost analysis of various systems
Epoxy Coat Garage Floor Coating | COMPARATIVE ANALYSIS