I've been sort of contemplating the same question. When I got started, I had a "only control no monitoring" solution by setting up a bunch of wifi-controled power strips, like
this (I liked the HomeKit compatibility in particular). This allowed me to control all of my devices via the iOS Home app, which is convenient (feeding? maintenance? push of a button in the app to turn on/off equipmenets). I also am in the Ring Alarm ecosystem, so I used a flood sensor for leak detection in the cabinet.
What this setup doesn't get me is to monitor temperature and pH (it seems the Apex salinity probe is not great and the ORP seems like a not useful measurement) and the ability to automatically do something if anything goes wrong. So recently, I'm looking at the A3 Apex and also wondering what to do.
My cost-benefit analysis:
The cost of my current setup is less than $100. $300 for monitoring with the Apex Jr. If I want monitoring and control, it would cost $600 with the regular Apex. Seems like a lot to pay $500 for just monitoring two parameters (not to mention the extra time and effort in setup).
A lot of the Apex accessories I don't find necessary or compatible with my 35 gallon nano tank. COR-15 return is way too big for a nano. Don't need DOS - expensive and I just need a simple doser for All-for-Reef. WAV seems too big and I like my Nero 3. Tridant is expensive and I don't need to test alk 4 times a day (if they can support "occasional" testing it would be convenient). List goes on. Seems like if you actually want to be in the Neptune ecosystem and all your devices are from them, then the Apex is useful (use the 1Link in addition to the regular outlets) and you'd save a lot of cables and different apps. There's also quality concerns - a lot of complaints online about cheap China build quality. The EB832 in particular had a bunch of failures and gets poor reviews. It's 1) harder to replace for me (if my HomeKit power strip failures I can get a same day replacement), and 2) I lose functionality (no more integration with HomeKit)
@Poochaku mentioned heater failure. I see two scenarios - if the heater goes dead (cold), this can simply be solved by having two heaters (no controller necessary since they will automatically adjust). If the heater goes crazy (hot), then you'd have to have monitoring and the ability to shut down the heater. How often does this happen? If this is a black swan kind of event, seems like it's not worth it to address. Is this worth addressing with an Inkbird? (seems their review isn't stellar either).
Is all of this worth the additional cost? I don't know.