Interesting , Good points by ldrhawke.
Zeo is a very basic system that does work, I quess most people dont like all the secret behind it. and the coral losses, Most people who use zeo have success, but then there are many that wont admit that they have had huge coral losses.
Many companies now also do zeolite which you can put in the filter, it does the same thing. The media even looks the same.
My experiance so far which acids/zeolite dosing has been that everything starts ok then total wipeout of all my soft corals and a few acros. This has happen 3 times. My corals did start to look good, but no reduction in phostphates and nitrates. Then i have tested some tanks using zeo and phostphates are almost zeo insome and still hight in others.
Like any product it has its pluses and minuses .
Hopefully soon we will see a zeo tank from NZ on reefcentral in the next 20 years.