They really aren't that far off these days. Certainly no 'nasty toxic smells/paints'. Brick fit/clutching can be a bit sub-par on certain parts, but is generally not far from the real thing.

Lego does a much better job of instruction books than the 'fake Lego' sets I've seen, though. Also, Lego has higher standards for the model designs themselves, whereas some of the 'fake Lego' model designs can be rather more fragile than anything Lego would release, which adds to the impression of poor brick fit/clutching (e.g. the Xingbao Xenomorph)

(Haven't seen any of the Technic clones, though. They're likely to suffer more from loose or poorly-fitting parts)