I guess working in the Meat packing industry has some advatages...
Polyclip and Tipper Tie are the only two manufactures that make metal clip tieing machines, I work with both at work, they are both equally reliable, though they can be tempermental, Once you get the feel for each ones idiosyncracies, they are very reliable and easy to maintain. Granted in my industry we work them much harder than they ever could be used in the aquarium trade. (continuously 16 hours a day 7 days a week)
That being said they are wonderful machines, I feel they are probably a bit expensive, and most require a high pressure air source, I would think a standard air compressor to run a nail gun would work. If you have any more questions regarding them (other than price) let me know.
---Rick