Yes, it is a DIY ATO.
Basically Tunze has it's "Osmolator" unit which sells for $202 on BRS. You can buy the same pump and the DIY float switch kit for $76 and do basically the same thing without the electronic programmer.
TUNZE Osmolator Universal 3155 - English
That being said - You can purchase the JBJ ATO controller and the Tunze pump for $102 and with the AL pump for $97.
So basically for $20-$25 more than I spent for the DIY (before buying the 2nd 12V transformer or the extension cord, so more like $10-$15) , you can get an electronically controlled ATO and a good pump that hooks up in less than (5) minutes and looks clean and nice.
Or you can spend an hour or two putting together a DIY kit, trying to make it look decent and have no electronic controller.
My vote in now wholeheartedly to go with a JBJ controller and an aqualifter pump, as the Tunze has to be hardlined in.
I will certainly find some use out of the stuff I bought, but not as an ATO for my aquarium.