I just read through the listing about it, and this is my take:
RK Elite $490 = Aquacontrol 3 $569
+ can control up to 160 outlets (AC3 controls 24 outlets)
+ good mounting options
- sending emails when Alarm goes off (my AC3 text msg's my cell phone when something goes wrong, this is the best feature of the AC3 IMO)
- ethernet module (no clue on price or date yet, it comes built in to AC3)
- web server (not mentioned on RK Elite, built into AC3, so you don't need any other software)
- feed mode button (one button press turns off the pumps I choose for the amount of time I choose while I feed, then automatically turns the pumps back on)
- ability to control Tunze streams (cost $175 for AC3 module, which is cheaper than Tunze 7096 controller)
- ability to update firmware over ethernet (must be done via USB cable)
On my 120 gallon system, I only control 6 outlets. I can't imagine ever needing more than 24 outlets to control. The only other benefit of the RK3 elite that I see is it looks cooler and has better mounting options. To have ethernet capability for the RK Elite will most likely get the prices right about even. So price is not really a decision factor between the two... but the other functions that the AC3 can do IMO far outweighs the benefits of the RK Elite. You gain the possibility of tons of outlets (which is doubtful would be needed by hobbiests), but lose vital functionality.
Long and short, If I was in the market for a controller, I'd buy the AC3.