Well, a Raspberry Pi is only as reliable as it’s power source. Power fluctuations will corrupt an SD card in a heartbeat. You could use MySensors to pass the data to Home Assistant and use an Arduino instead, which is far more reliable. The probes that the Apex uses are just re-branded Milwaukee Instruments probes that can be bought for a fraction of the price, and there are plenty of other options available, though.
While I completely agree with you, and prefer to have hardware dedicated to a task that does a good job of just that one thing, the Apex is not that box. Without disclosing too much, the vulnerability that I discovered is essentially a flaw in the network stack of AOS where it simply cannot handle certain types of traffic and crashes the kernel. This led to all of the relays on their power strip flipping on (meaning my heaters, lights, pumps, everything turned on at once), and the controller completely locked up until I manually power cycled the unit. (This also means their power strips are wired to be normally open, which is a really really bad idea in this case.) While testing my hypothesis, I could fairly reliably replicate the behavior. This is why now it sits in it’s own dunce corner VLAN, isolated from the rest of the network, and the only thing it gets access to is their AWS IPs for ApexFusion. Neptune Systems’ decision to sweep this under the rug has led me to discontinue supporting their business.
If you haven’t already, look into the Reef Angel systems. They are also standalone devices, but they’re also completely open source. Their platform has support for MQTT, meaning you can instantly tie it into Home Assistant with zero effort. While their app’s user interface might not look as pretty, the system’s reliability is far higher, and I have met several people who have had nothing but praise for them. Neptune Systems is all marketing gimmicks.
I’m sorry if this news upsets anybody. I know there has been some other interest in this, but between the closed nature of the Apex ecosystem and Neptune Systems disregard for the security of their product, I would advise you look elsewhere. If you already own an Apex, you can take a crack at parsing their status feeds, but it’s unfortunately not worth my time anymore.