There is a difference. In DIY logs, many have explained the difference between 2 versions of mx5021. Point comes here that there are 2 versions of mx5021 but unfortunatly I am not sure if the mx5021e is considered as second model or they redesigned mx5021's model. But the sound quality is pretty much the same though the second version of mx5021's buils quality has dropped down:
The newer batch of MX 5021 has a totally redesigned subwoofer and midwoofer cone. The cones on the newer ones are spherical with no flat surface on the centre whereas the old ones has a flat surface in the middle of the spherical cones. Other than that the crossover circuit is different and one of the opamp which some say is a good thing- but still the output is the same so it doesnt matter much.
In layman's man out of the 2 get the cheapest. But also make sure you have a good sound card as well to get good output.