Like the desert eagle hath said, there are tons of reviews. I looked at this brand when it first came out and concluded it was indeed "too good to be true." Who doesn't want to save money? (I focused on spinning reels. I did not research baitcasters.) The problem with positive, glowing reviews is that they are written shortly after purchase. I would like to see some long-term praise; but it is not happening. There was a hilarious review, somewhere, about the new Sharky series--written on a site where the entire right margin was splashed with Kastking advertising.
Most times I'd say you'd get your money's worth on a $50 spinning reel if it serves you for a year, maybe a year and a half, longer if you maintain it with religious devotion. I would not say that about Kastking spinners. One example why: Two years ago Walmart and similar outlets advertised Kastking Orca IIs at somewhere between $55.98 and $61.98. You could get the same model wholesale (if you bought 20 in bulk) at $13.85 each. Cheap. For sure. That model is no longer in stock. Among the gripe reviews there was/is a common thread about some of the reels falling apart right out of the box. That's never good and should send up warning flags. As said, we don't have a lot of good reviews from people who've had Kastking spinning reels awhile.
As for durability...much plastic, so keep them out of the sun and they won't melt.