you can get 2nd hand 18" CHs for around £700 if you look hard enough. considering that reps will cost about £400 but will be worthless when you come to sell them, or you spend £700 on CHs which will still be worth what you paid (if they're still in good condition) then it's a false economy getting reps
and as above, they'll disintegrate when you come within 6ft of a pothole, some can be hard to balance properly, the paint finish will be poor and a lot need refurbishing after a year or so AND they weigh more?
i'm sure that there are some reps out there which aren't bad - which look original and are made properly. but you can't tell which are which so i wouldn't take the risk personally