I have 1 m and 6 f in a 60 ltr. I never intended to keep both sexes together, as I was very much in the "males should never be kept with females" corner before this. They were all bought as juvenile females, but two turned out to be a short finned wild type males. I re-homed the more aggressive one, and I was originally going to separate the second male, but a betta breeder I know who specialises in short fin types suggested it could work out.
I think whether it works or not depends on many factors. The personality of the male you have is definitely a big factor in whether it can work. My guy is pretty laid back compared to the long finned males I've had in the past, and the females will happily stand up to him if he gets a bit too stroppy. The females do more damage to each other than he does. He'll occasionally flare and chase, but the females will actually nip each other. Secondly, they've all been together since they were tiny. I've heard from a few betta breeders now that if siblings are kept together there's a better chance that they can co-exist once mature.
Another reason I think it works because there are 6 girls, his aggression is spread out rather than it being focused on just one or two individuals. I have a spare 35ltr as an emergency back up if he decides to turn nasty, but they've been together for 7 months now without any trouble. I destroy every bubble nest he builds, just to be safe. And lastly, there's a big piece of redmoor root in there with a crazy load of java fern attached. There are loads of hiding places for the females to escape to, but even with keeping a group of females by themselves it's recommended that you have things in the tank that will break their line of sight.
Over all, I wouldn't recommend it if you haven't had a fair amount of experience with bettas in the past. If you do want to try it, I would try and get a large group of very small juveniles and raise them together, see how many turn out to be male and then keep the most placid whilst re-homing any others. I think a big key to it being successful is having enough females. Having just 1 or 2 with a male is asking for trouble, IMO
And of course, make sure you have a back up tank just in case.