Dragging/pulling sled

Anyone used one of these for cardio?  If so, how did you find it?  I'm worried about the racket it might make and whether it would damage the pavement! 
 
Also, how much weight did you use and what sort of routines did you do?  How often etc...

I bought a Prowler recently. Got it from Wolverson Fitness, cheap and there is a similar priced one on Strength Shop too.
 
My garden is fairly long, about 16m and I got some 2m wide 'turf protector' which is basically a roll of plastic mesh to top it just becoming a mudbath. I run pushing shuttles for intervals. I love it.

Thanks Chris. That site has some very desirable things on it!  I'm really strapped for cash so was just looking at the basic metal sled from Strength Shop as I don't want to fork out the money then find I don't get much use out of it.  The other thing putting me off is the cost of plates.  Gee whizz...flipping expensive or what! 
 
The turf protector is a great idea and I may be stealing it!
 
How often do you use the prowler and do you push it on training days?  I've been doing 5/3/1 for ages but have never done the cardio recommended so I'm thinking off giving it a go but not sure how I'll react to 3 - 4 sprint sessions. 

slap a bit of wood on, get some baags of sand from wickes for £1-£2 they weigh 25kg I think and stick them on the wood to stop them falling through your prowler and hey-presto, same effect as expensive plates

I've just started 5/3/1, do it mon, wed, fri and push the prowler tue and thurs for 30 mins, minute on, minute off.
 
As I understand it the whole point is that it can be loaded to target higher intensity/shorter duration work than most CV without the eccentric phase microtears that weights cause so less recovery strain.
 
So far this seems true for everything but calves!

Start slowly and build up. You will be surprised how quick you get better at them.
We do 40kg double length of the gym then recovery is 2 x double length of gym. Our place is quite long with a straight run through.