I have an RK II. I probably wouldn't have bought new at the $300 price (shipped), but I picked mine up for $150 and feel it is well worth that. I use it to control my light cycle, temp, and my pumps. Yes, it is a basically glorified timer, but it is digital, has battery backup, and is extremely easy to program, plus it has overtemp safeties which timers do not. The pH probe is just a added perk (which I am currenlty not using since my probe went bad). I think having the controller send an email would be a great add on feature, but I don't really have a computer to spare, or want to leave one running 24/7 to accomplish this, and in most case there would really be nothing I could do with the information that my RK II isn't already going to do (namely overtemp protection). I would definately keep and eye out for used RKII. I just sold one a couple of weeks ago for $150 so they are out there. The only parts that I have seen go bad are the pH probe (which goes bad no matter what over time), and the backlighting.
I guess the more elaborate (valuable) your setup the more you could justify in spending on a controller, but with my tank I just cannot justify it. Then again if my tank crashes I will be out about $200 in fish and a silly anenome so it really isn't the end of the world. If I had a tank like Cindy's I would probably fee different.