Hope your handy with the tools, have been running the same unit for 5 years now, they're great once you get the chainline set correctly, otherwise they can be a bitch.
On the bright side when they are set up ok, they are smooth and quiet to the point that you dont even notice they are there and they are infallible, they will never fail!
Oh the guides rollers are a plastic/nylon and just run "loose fit", so they can get gummed up and wear pretty quick if your not one of those people you clean the bike after each ride. I ended up making my own rollers out of teflon
The replacement nylon guides are usually over $100 alone, which Im almost due for, but these days I think the Gizmo's are out dated and dont really compare to the E13's which i'll be changing up to once this set of guides wears out...
er Having said that $100 for the whole unit... DAMN!
Where???