I have never flown HO in biz class, but fly them in economy often.
In general, I am not a fan. That having been said, Shanghai Airlines, and Spring Airlines aren't really any better.
My main criteria for Thailand flights is timing; the Chinese airlines seem to prefer red eyes, which I greatly dislike. Basically, if the choice was biz class on an HO red eye v Y on a TG daytime flight for the same price, I would go with the latter.