Not bought a fly rug from them but I did buy my summer lightweights in their BOGOF deal. I'd say they are very slightly smaller than weatherbeeta - but fit my fine TB better. Smaller round the neck, as opposed to WB which is more of a low cut dress type of rug... Not much, but hope that helps.
Ive just had the 2 for £25 deal, ordered no problem 2 lightweights which for the deal is a very good offer, evn if my horse demolishes them this winter then it would still be worth the price as he rips expensive ones just as much!
I got the fly rug last year, it was a nice fit, right size, but the chest was tiiinnnnyyyy! would have fitted a skinny tb alright but even my 2yr old chest was too wide for it, he is a tb x conny, so not massive! but otherwise it fitted nicely everywhere else!