I didn't do every calculation. I was just showing how since winning pays a lot less I don't really see the advantage
it comes out to roughly the same as playing a normal parlay at another book, apparently
Winning one combination pays less. That doesn't make it worse or even equal to full parlays.
Let's say you had two dice.
If you were to pay for only rolling a 12, what would fair value be? You have one combination out of 36. So, it would be 35/1.
To verify, let's find the expected value: (35*1/36)+(-1*(1-(1/36)))
That equals zero. So we're exactly at fair value.
Now, if you add a pay for rolling a 7 too, the probability of rolling a 7 is 6/36 or 1/6. So fair value would be 5/1.
However, now, if we try to pay fair value for both combinations, look what happens to our expected value....
(35*1/36)+(5*1/6)+(-1*(1-(1/36)-(1/6))) = 1
Whoops. Now if we're the house, we're paying +100% EV. We're gonna go broke real fast paying fair value for each leg.