Remmeber k'nex? Building a tank was like playing with k'nex. Adding an apex is like motorizing those k'nex. Are they fun without the motor kit? Sure. But with the motor kit, oh the places you'll go!
Really, I couldn't imagine running a complex reef setup without an Apex. This has saved my tank on a number of occasions, aside from the general increase in usability and simplification of most tasks. I use the app on my phone, I was away on travel, and couldn't connect. Come to find out, the breaker to my tank tripped, and if not for the Apex, wouldn't have known. Was able to get my wife to go downstairs and reset the breaker before anything was lost.
Can you do this all DIY? Sure! But the cost of the Apex is FAR less than the cost of my time would have been to set everything up, DIY.
And for the money you'll spend anyway, just spend a couple bucks more and get the Apex. A quality ATO system, with redundant floats, timer limits, etc. is going to be pretty pricey. For just a bit more, you can get an Apex Jr., set up the same ATO system.