I would say a useful book for offline play but be wary of relying too much on tells, in practice getting a sure read on somebody is not so easy. In general I don't really like Mike Caro's style of writing I have to say though I admit I need to give him more time, the book though a new edition looks fairly dated as well. Don't think there's any real alternative tell book out there as far as I'm aware though so it's certainly worth getting if you play in casino or home games - in fact home games is probably where this could really be a very valuable book where getting a tell on somebody should be much more reliable.