If everyone likes the mixed cards and improved flow, i don't see the harm.
The fact that we sellout our events, year after year, speaks volumes IMO. A well run tourney is reason to come back.
No harm if everybody likes it. Doubtful that
everybody likes it, though. There is a lot of cover in a sellout, though many may love the event
in spite of the mixed groups. Those who don't, have the competition manual to back them, and it's quite a stretch to squeeze uniform lunch times in into the practicable exception. One benefit of playing a sanctioned event is the expectation of standards, including this one.
I've played events that did this---and, further, mixing in the pros---and my feelings, and those of people I spoke to, were mixed. I enjoyed playing a round with people I'd never otherwise get a chance to, and in a small division, not ending up with the same people all 4 rounds.
On the other hand, some prefer to be grouped with the people they're competing against. Some, particularly we older folks, like our divisions, in part, for the company we're keeping. Some beginners and weaker players feel intimidated being grouped with much better and more serious players; some better and more serious players don't want to be saddled playing with beginners and weaker ones.
For those who love it, great. For those who don't, the trade-off for a shorter lunch break may not be worthwhile. Which isn't to say they won't love the event, overall.
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And with all that digression, I agree---and least in events that don't fill---that TDs should set up groups to speed things along, where they can. For slower divisions, smaller groups, and if you have major backup holes, try to get the slower divisions through them early in the round.