Ive never had one myself, but i did inquire about them one time. I was told that they are very good. too good in some ways as the mechanical cartridge is almost too efficient and needs changing quite often- every 1-3 days in some cases. Thats fine if you can have multiple cartridges to switch out all the time, but they are not cheap. You would either enough so you could wash a load of dirty ones in one go, or if you only had 2 or 3 you would be forever washing one at a time. On a positive note, the mechanical cartridges can be removed/replaced without breaking the filter down. like ecoli said I was told its an expensive gadget, reads conductivity, which is fine of you use that to monitor your tanks, but pretty usless if not. Has a flow meter, but thats just a fancy gimmick really- I had a flow meter on my old canister, my eyes! I could see when flow rate dropped! I was basically told that unless I didnt mind the cost of the cartridges, and unless I really wanted the digital gimmickry then i had just as well go for an fx5 or similar. They do look cool though, and i believe there are options for various cartridges other than mechanical, which again are expensive and i believe theres a reasonable amount of bio inside.
Again, not my personal experience, but advice from a trustworthy lfs manager at one of the best lfs around here. Although he said they were good he actually said that i would be better off with an fx5 so he wasnt just trying to sell me the more expensive system. He told me that when they first came out he had people bringing them back after 2 or 3 days because they werent working- the problem though, was the mechanical cartridge had blocked up!
Hope that was of some help, I think it boils down to individual people... If money isnt an issue and you are happy to buy several different cartridges as well as well as different types of cartridges. If you want the technological side of things and need to know the conductivity etc. if you need a smart looking filter to be in the open. Go for the G series. If all you want is a proven workhorse thats gonna be a filter and nothing else and is going to be hidden or not in a room where the aesthetics of your filter matter then stick with an fx5/6.
