This is a small dust brush that extends from its plastic shell and locks into place.
The hair doesn't look or feel synthetic, but I don't know if it is or not.
I have a large round headed synthetic cosmetic brush that I've been using for dusting off models, which is comparable in price.
The Gunprimer brush is more springy/stiffer and it's more compact, so it's definitely easier to pack and bring along.
This is preferrable to my cosmetic brush for cleaning after filing, to remove plastic dust, but for cleaning an entire model, the larger handle on my cosmetics brush and the larger head allows for you to clean the dust off of it much quicker.
You could probably use it as a very good drybrush for large projects (terrain), but I don't know how well the bristles would fare in the long run.
Full marks, nothing wrong with it, you get what you pay for (arguably more if the hairs are indeed real), it does its job well and I think what matters most to some people is that it fits in with their other hobby stuff.
It'd been prettier in a black gloss with letters embossed rather than the clear plastic with a sticker, but that's me nitpicking.