10 days just isn't enough to absorb it all properly. A couple of examiners I've met told me that they've been less than impressed with the products of these courses. Anecdotal evidence, I know. The 10 day courses are mainly aimed at ultra busy business people who just don't have the time to do it "right." I'm not against accelerated training (did my PPL in 21 days) but given the choice I'd take my time with the IR, 4 weeks or so. Remember the IR is the cornerstone of your professional flying career so it's important it's done right. Also, these courses have you take the test in a single which does not give you multi IR priviledges. You have to take another (very difficult) test to get a multi IR which makes it expensive overall. Oh, by the way, I'm an IR instructor myself.