I have been an Apex user since they first came out. They will not fix all your woes with some magical computery goodness. However, I find them to be invaluable, and wouldn't run a reef without them.
Pros:
- They can monitor all kinds of various parameters, like ph, ORP, salinity, and tell you when something is out of whack.
- The Fusion interface lets you see this remotely, or sends you alerts when something is not quite right.
- The Fusion interface is *really* nice. Lets me track things like manual measurements, set reminders to change filters. Love it.
- Water on the floor sensors, or high/low water sensors tell you when plumbing has gone awry.
- You can write simple code to deal with problems. For example, temperature too high, shut off all the lights and heaters.
- If you are a control freak like me, you can go absolutely nuts with the programming and do all kinds of crazy things with them.
- You can have far better control of fiddly equipment like calcium reactors, rather than sorta guessing at it.
Cons:
- It's a piece of equipment like any other, and must be maintained. You need to clean and calibrate the probes. You need to check that salt isn't getting on the connectors. You need to verify none of the sensors are going bad. This can add to your chore list.
- It's easy to become over-reliant on them, and trust it more than your own eyes. You see the pH in the display as 8.0, but the corals are all sad, so it must not be the pH. It might be the sensor gone bad.
- If it breaks for some reason, you have all this stuff that was automatically controlled and you are scrambling to figure out how to operate it.
- You can become complacent, and trust computers more than mechanical failsafes. For example, you set an ATO up using water level sensors. Maybe you were even smart and put in a few extras. Your programming is flawless, your sensor placement is perfect. But if the sensor fails, you have a flood.
Basically, they are amazing pieces of technology, but don't let yourself forget it's a computer and computers have bugs or break or little bits of electronics die in annoying ways. The pros far outweigh the cons, because most of the cons are your fault, not the computer's fault. For someone who travels alot, I would highly recommend it. Especially if you have a spouse at home taking care of things. You can look at the Fusion interface, and say "hey honey, can you do a <blah> test, or look at this thing?" Or maybe the spouse says the tank looks bad and you can say "oh, the pH is out of whack, go do this".
Recently, mine has saved me from two leaky pumps. Woke me up at 3am once, and another right before I left for work. One of those had the potential to be catastrophic. And because the pump that was leaking was under the control of the Apex, even if I was at work, I could have just shut it off. Easily saved me $1000 in damage that day. Already paid for itself.