Some of these brands may offer more than one mandola model. If so, the "generic brand Korean mandola" is usually the cheapest one in their catalogue.
One important thing to keep in mind is that the various brands aren't necessarily absolutely identical. There may be minor design differences and there may also be some quality differences depending on how good the distributor's quality control is. It would be interesting to know the rejection ratios they operate with, but there's not much chance anybody will ever tell us that.
How good is it?
The Korean mandola is quite a decent low-priced instrument; a good design, made from good wood and built with a very stable production quality. It can't match a top-quality handmade instrument of course, but that's not a fair comparasion at all.No matter what name there is on the peghead, this is a decent beginner/intermediate mandola with a solid spruce top, solid maple back and sides, rosewood fingerboard, gloss finish and a slim, playable neck. It can't compare to a professional, hand-built instrument of course, but for less than 500 dollars it's well worth the money. (I've heard of them being listed for up to $750 though, and that is daylight robbery!)