Probably a waste of money.
Things that can kill your fish:
(1) Temperature. Tons of low cost temperature monitoring solutions out there.
(2) Salinity. Salinity monitoring is notoriously poor on controllers. Probably better just to test occasionally.
(3) Water quality. Its pretty costly to get into automated nutrient testing. Also being FOWLR you have a much wider range of acceptable. Probably just better to test occasionally.
None of those things would sell me.
I guess then you look at convenience. Having everything in one app vs a bunch of standalone options. I can put up with a dozen apps on my phone to save $400-600.
Leak detection? Third party options as well...but nice to have it integrated. Like if you detect a leak, turn off all the pumps type situation.
If you have a larger tank maybe the ability to do automatic water changes...but that's a whole other can of worms.