I think Music On is a really well-marketed party with commercial appeal whilst masquerading as an underground club night. In my opinion, it hasn't been that since 2012(ish).
The crowd isn't too clued-up, and a lot (at least a lot of the young Brits) are going because they are told this is the in party (and it's hard to argue it isn't).
And of course fiercely loyal Italos make up another large contingent. They probably go not so much for the music - which has got v.diluted in the past 2 years - but more out of a sense of camaraderie. God-like worship is pretty apt. But sense of community tells a part. The Italian workers feel this is as much their island as anybody else's.
Their "guestlist" is a mile long, and gets the punter in nice and early. So they must be doing something right.
I've had some great nights in there down the years. Though, I must say usually well after 5am when the chaff have called it a night and there's room to breath.
The most bizarre thing I find - as other's have posted above - is that in the videos that get posted every Saturday, the crowd look incredibly unengaged.
And yet they get shared in their 1000s.