As for NDI, it is a rubbish organization, and any recruiter who places an FT with them is a crook.

Indeed, NDI is as bad as you say. But that poster who's complained has bad English. I've read some of his contributions. Maybe the recruiter he used coudn't place him at a proper school on account of that. But I wouldn't go as far as to say said recruiter, whoever he is, is necessarily a crook.
Recruiters are generally lazy parasites, that's true. But so are school/uni FAO's as a rule. Just look at the jobs board for China. If you ignore ads for training centers, and those placed by recruiters, which often include training centers, you're not left with many job ads at all. In fact, very few indeed, and some of them are for private schools, or private/public partnerships, which are basically private schools in regard to how they treat their FT's. Then ignore the international school ads, and you're left with relatively few public sector employers' ads, the best option for many of us, provided that our English is not too bad.