Which CO2 Controller to buy?

So i'm getting ready to buy a CO2 controller, but not sure which one to get..
I want the kind that automatically keeps the CO2 at peak levels.
I will be using compressed CO2 tanks.
Also, temperature is not an issue, so I dont need a controller that integrates that.
So basically im just looking for a good automatic CO2 monitor/controller with photocell.

Based on my research, ive got a few options..

-Titan Atlas-1
-Titan Atlas-2
-CAP PPM-2A
-Sentinel CPPM-4
-GreenAir SPC-1

There are other options, but they dont have photocell, or there include more stuff i dont need.

I dont care about anything fancy, or being able to "set" my PPM, i just want it to do it for me.
Im leaning towards the Titan Atlas-2 based on price, and it sounds like what im looking for..

What do you all think about these controllers?
And what can anybody say about the Titan Atlas-2?

Any info, feedback, or suggestions would be greatly appreciated! Thanks!

i got the ppm4 and im not too stoked on it.. but it was 270 bucks vs the fuzzy logic badass one for 6 bills. so if your looking for cheap.. i guess it gets the job done.