All of the issues I described are related to how Neptune has the alarms programmed for stand-alone use, and as I said, mounting the backup sensor higher in the sump would eliminate some of the issues. If you have an Apex, then you have complete flexibility over the alarms and behavior of the ATK. I recently purchased an Apex and plugged in the ATK to replace my Tunze. It was incredibly easy to set up, seamless, and the fact that the PMUP can use a 24V port instead of a 120V outlet saves space on my EB832.
I don't think the mechanical float would damage the pump, and the pump should shut off after 5 minutes, regardless. In the off event that something has gone wrong and the other safety mechanisms aren't working then potential damage to the pump is an easy trade off for a potential flood.
I did some testing with the ATK, and the optical sensor requires about a ⅛" drop in water level to switch on/off. When I checked the Tunze, it was actually slightly more sensitive, but they're both plenty accurate, IMO.
In using the ATK, I've found the hardware to be solid. The only issue I've seen is from someone using Kalkwasser (The kalk would clog the hole in the float valve, clog the hole in the siphon break) The clogging issues can be eliminated by removing the float valve and siphon break and were issues with Kalk more than with the equipment.
The ATK doesn't come with a sensor for the ATO reservoir, but the FMM that functions as the controller in stand-alone mode has 2 open ports that are designed to handle a leak detector and an optical sensor for the reservoir. (They're about $30 each, IIRC) All you need to do is plug the optical sensor in and mount it in your reservoir and it will turn off the ATK when the water drops too low. Both those are nice features that I haven't seen on other ATO systems.