I did lots of reading before I made my mind up. There are differences for sure. What made my mind up in the end was the layout of the PC4 bar vs the Energy8 bar, the light controllers, and a couple other things. Don't remember right now.
I'm just trying to help you become more informed.
You won't hate the RKL, or the RKE.
Many would bash me for not selling you on an Apex.
It's a great unit too. I didn't like the fact that the starter unit was over $300.
There are others too, such as Profilux and another that isn't coming to mind.
$130 is a great starter price, but inform yourself first.
And keep in mind that I didn't cheap out, I just bought what I liked. It still cost me over $500 for my RKE with some other goodies, and I started with the same thought you have.
http://www.ghl-direct.com/
http://www.neptunesys.com/
http://www.digitalaquatics.com/