I have the sherpa without the hood, it's the best rug I've ever owned! I spent years struggling to keep weight on my Arab over the winter, first year she wore the sherpa (under her NZ) she was actually slightly chubby coming out of winter!
The tail flap is massive which is great for the show horses but if you're using it as an under rug it easily folds up over their back (otherwise it would end up covered in mud as it's much wider and deeper than an NZ tailflap).
The top of the neck is elastic so they can't roll the neck down and get themselves dirty, plus it stops any heta escaping.
The belly cover is just the cutest thing every, I call my rug and onesie as she looks like a kid in a pyjama suit when she wears it!