I was sitting right where you are about a month ago. I purchased a JBJ, but then before I even received it, did a lot of looking at controllers and quickly realized that I could get a controller, with a small aqualifter pump and float switches for just a bit more. I did, and am so grateful I did. I don't know if your budget would make that possible, but honestly, even a JBJ costs enough that something like an Apex Jr or Reefkeeper Lite + the float switches won't be a whole lot more and give you so much more that an ATO by itself.
My ATO is an Apex Lite, with a self made wire instead of the break out box for the float switches. I purchased the Reef Keeper dual float switches and a Toms Aqualifter pump. Works great, plus I get all that a controller offers in addition, including emails or text messages when my ATO needs water!
Hope that helps. If you want a simple ATO, Tunze's is great from what I've read and researched, but JBJ's seem to be pretty decent too and are less, which is why I went that way, or almost went that way.
