The tunze is a good one for the aio's because it is more sensitive...
I LOVE the Red Sea max AIO's but yeah$$$$
I think your fail safes sound right, they do just need to be updated and checked monthly...
That's pretty much the only reason I have an apex,lol water leakage, heater breakage, or power outage
Just don't get discouraged... We all have bad days.. I just made 10 gallons of water on the floor of my spare bathroom, thankfully it's in the basement (as is my tank)