HM is polygenic (MULTIPLE genes involved) and even HMs don't breed true (they make lots of Deltas and Super Deltas... From what I've been hearing from breeders MORE of them than anything else... True HMs will be the minority of your offspring even with 2 HM parents)
From the breeders I've been talking to, they say VT us dominant to pretty much everything else. So offspring will likely consist of mostly VTs and an occasional Delta or SD... At least theoretically. And really there isn't much demand for the offspring you'd end up with (numbers wise anyway) so you'll have to be prepared to do some heavy culling or try your best to give them away.
The smart money (no one gets rich doing this) is on getting a fish with a unique and special trait and attempting to multiply it, or combine that special feature with something else.
I'm currently importing a couple "BIG EAR" Betta (extra long pectorals) to try and enhance my whites with it, as well as helping my friend develop CT Big Ears (he is hoping for "FW lionfish" look out of it) it should be interesting
But the trick (from a PRACTICAL standpoint anyway) is what you are going to do with lots and lots of fish, many of which will be "defective" (because they do produce birth defects... Among other issues) or simply "not marketable". Which means your stuck with them... Which is either a lot of wasted fish from flushing (no offense) or a whole lot of water changes!
It's fun and interesting, but you always have to try to keep your mind on the bigger picture. Let's be honest, there is No SHORTAGE of Bettas! Which is why if your going to make more of them, we have to be responsible enough to either a) breed a specific kind that you happen to love b) a variety that is in demand so that you can "move the extras" or c) breed something rare or uncommon because it is the oddity. Or D) ALL of the above.
Not trying to talk you out of it, because it is fun and cool watching fry grow or fish do their mating displays, but it can also be hard work and heartbreaking if you have a sudden fry die off, or the male KILLS the female (or vice versa... One of my white females killed my black/Melano rose fin HM male recently, albeit in an unconventional way) it can be a great big heart breaking headache as well, so it definitely takes the sting out to have a plan AnD a back-up plan or two... Just in case they go "off script" at sone point; because REALY, how often do things ever go "according to plan"?
I'd get a dragon or pastel just to work with something just a little different
