I don't own or use any commercially available controller system, but I've had some exposure to most of them over the years. Take my feedback with a grain of salt, as it comes from my heavily-DIY biased perspective and I'm likely to be harsh about things that most people might not care about. After all, one of the reasons why I DIY'd my stuff is that I don't really care for any of the currently available products. As far as I am concerned they all have some pretty serious faults.
Reef Angel: New, small customer base, all your eggs are in one basket (Roberto IS the manufacturer, support team, marketer, vendor, developer, etc.) Yes there is a community there, but the community isn't obligated to help if you have a disaster and there's a certain risk level for a one-person company to fail if that person goes on vacation, gets hit by a bus, gets a job offer they can't refuse, etc. Plus, this hardware is inherently based on a very, very simple foundation. If you just want the basics, that's probably OK, but there's a very real limit to the future growth of the system. Arduino is an amazing platform but compared to the technology that's emerged in the last few years it's kind of a Flinstone-era relic. Also, the hardware design is hard for me to follow sometimes (i.e. certain features are included in the head unit that I would have expected in a separate module to keep the cost of the head unit lower, etc). For me, the only advantage of the RA is access to the firmware, which for MOST people isn't really an advantage. With closed source controllers, you're basically writing or configuring pseudo code that the actual firmware interprets, which gives the manufacturer the opportunity to catch or prevent serious mistakes because they don't let you into the actual guts. The danger with open firmware is that YOU, potentially, are modifying the actual firmware, there's no "filter" (unless you use one of the "wizards" or code examples the community has developed, in which case you're trusting someone with no accountability to control your reef). And when I say serious mistakes, I'm not talking "oops I left the lights on all night" but rather "oops the buffer for the wifi module I just added overflowed because I used the wrong variable when I called it, and now the controller crashed, and every piece of equipment on my tank is in an unknown state."
DA ReefKeeper: In many ways, a closed-source equivalent of Reef Angel, but with a more well established vendor. Same inherent hardware limitations (wimpy processor). Some poor hardware design (IMHO) in some of the components. Compared to the RA, it's less flexible (though this only applies if you're willing to go rewrite the RA's firmware yourself) but coming from a more established entity.
Neptune Apex: Also a more established entity. Doesn't have the same core limitations as the other two (it's built on a much nicer and more powerful processor, which theoretically leaves more hope in expandability over the coming years) but there are, IMHO, some pretty serious faults in some of their hardware designs.
There are definitely others out there but IMHO most of them are either not well established in the US, have weird feature sets, or are grossly overpriced.
The one common thread here is that (IMHO) all three of these major players have odd/poor hardware design in one or more components of the system. When you're designing a hunk of embedded electronics that's going to get thrown into all kinds of different environments by hobbyists who might not be electronics experts, IMHO, you'd want to design to a VERY robust and fault-tolerant level, and I don't really think any of these three vendors have done a super good job of that. With all of these controllers, there are stories here and there of people having sensors reporting strange values (poor circuit design i.e. the amp for the probe isn't well enough isolated), relays not properly turning on or off (poor parts spec and/or incorrect design for a given type of load), interference being caused by other common reef electronics (an MH ballast that causes a controller to flip out - I mean, cummon - if you're designing a controller for a reef tank it should be able to sit next to a major brand MH ballast without the end user having to put a faraday cage around it). For MOST people these issues probably won't surface, but IMHO they point to these devices, for the most part, not having highly rigorous designs (which would of course drive the price up).
I'd be willing to bet that the landscape for reef controllers is going to change pretty significantly in the next 2 or 3 years. It seems pretty clear that there's going to be a move away from 8 bit processors at least for the more serious contenders, and I'm hoping and praying that they ALL figure out their hardware issues by brute force of responding to customer issues over time (or a new player comes into the market who doesn't make these basic errors). If you're going to dump a ton of money into a specific brand, make sure you understand the future and potential for that brand and you're comfortable buying in to it.
