No, some of them simply aren't good finishing stones. And these are the ones that harm their reputation, because they can be more hit and miss than other types of hone. There's a few really good threads on them that I'd link if I were on my computer and could easily find them. But they've been tested pretty thoroughly and it's well documented. The good ones are pretty darn good, the duds aren't. There are visual cues and hardness variables that allow one to differentiate but Woodcraft and Ebay sellers don't care to separate the wheat from the chaff so there's about a 1 in 3 chance the stone you'll get won't improve anything over an 8K and may even degrade the edge.

I was lucky with mine as well. It performs very well, and is one of my favorite stones to play with right behind my Welsh Slates.

If the $3 yellow stone you're talking about is the one ZY sells, I've got one of those and it performs OK too. I just dislike the earthy smell it has. But it gave a passable shave that was an improvement in comfort over my 8k stone.

There's definitely no confusing the 2 though. The Guangxi is the better of the 2 stones imo.