It is really good quality, lovely and warm and is waterproof. It also has the added benefit of being fluorescent. I would definitely recommend it.
I also have this one in the tradition Newmarket colours, for hacking out on cold and frosty days when it isn't raining as it is really warm and looks really smart:
I have the horseware newmarket wrap-around one (ebay bargain) and it is brilliant. I have even been caught in the rain and my mare has been dry underneath it. Their sizes are slightly different to normal exercise sheets, you'd probably need the 4ft7 for your horses if they are in 6ft or 6ft3 turnout rugs.
I have the Mark Todd Fleece wrap around exercise rug which is really nice, a Mark Todd Fluorescant wrap around exercise rug that is waterproof, and a Witney woolen exercise blanket, which I've had for years which is great in the cold weather, lovely and warm!