I agree with thedarkhalf, save your money and stick with mono. It has way more scientific backing... we know it's effective and safe, whereas the creatine ethyl ester in "cell mass" is much less-studied and more expensive.
Creatine Mono is creatine mono IMO. The only difference i've seen is that primaforce has a creatine mono that is more like a fluffy powder and mixes much better in water and dymatize/met-rx/etc have the usual granular creatine. Both work well. Mono is mono.