5.3 is a Super fit for my 13.2hh Welsh sec B.
I love these rug I have one for my tb aswell as they are amazing. They are on the larger size so I went a size smaller.
I have used this everyday since it arrived and initially appeared to be great quality, design and fit. However, after the first week the elastic under the tail flap started to fray and a long piece of thread wrapped itself around my pony's tail. Also I noticed the stitching on the velcro of the neck cover has come undone. Such a shame that the finish is so poor on such a brilliant rug.
Excellent rug. Fits well and is very strong. The only trouble is when it is really hot the horse heats up a bit so could be a bit more breathable for really hot days.
Good quality however very big clips round the back legs with under tail strap clips also. Using for a shetland very tough material and keeps flys out.