I'm not a member, but I know several current and ex members, mostly in the UK, so here's my take:
If you are willing to put in the work, and there will be a lot of it, they are a genuine magical order whose their training seems to work - every long-term member I've met was at least a competent magician, and most were pretty good in one or more fields.
They do - in my opinion - gate-keep pretty seriously, especially if they decide that you are lazy or an idiot, so if you consistently fail to put in the work they demand during their trial phase, you won't be offered membership.
Most of both the current and ex members I know seem to have a good opinion of the IOT, which makes it pretty unique, because the ex-members I know from every other group - the OTO in particular - do not hold such good opinions of the orders they have left.
From what I can tell, most members of the IOT have a pretty dim view of personality cults, although some ex members (Pete Carroll for example) have been accused of trying to create one. These attempts have largely failed due to charisma deficiencies among the individuals involved, and fairly ruthless piss-taking by other current and ex members of the IOT.
