Btw it's always interesting to see djs put up a show when basically switching cds and doing some beatmixing :-pHere in Germany we don't like those David Guetta-esque DJ's, too.
Hoooray! You're the first one to mistake me for an non-German, ever, after reading my English :-p ... actually I'm also German, Berlin to be specific, so I had a good look at the club scene for the last decade... but before my photography days, so sadly I never came around to try what you did.
And that is my point in all these first and second curtain comments, 99% of the time you can't tell which was used so how important a feature is it really?
I could return the favor by saying that the other part concerning many topics (2nd curtain, auto iso, af, mp, dr, 2nd cf/sd slot) boils down to "If Canon doesn't have it, it can't be useful, and if you miss it you're no good at photography" ... but I don't say that :-), instead ...
I'd love somebody to actually post some images they took that illustrate how first curtain sync ruined their shot.
... I would like to point out that I wasn't talking about "ruined" here, the shots look fine as they are - I was wondering about the difference and as I know the Yn triggers support this somehow I was asking if he used it. This question alone proves that I don't think that there has to be an immense difference.
For his setup, 1st curtain probably is even better because he freezes what he sees when he triggers the shot and the dj was barely moving, but for a dancing club crowd with long-term ambient + flash I'd wager to guess that 2nd curtain would look more natural.