I've hit a number of non open parlay's in my betting career totaling over +150K the last 20 years, my parlay winnings is basically the only reason why I'm a profitable sports bettor, yes I know that is not typical.
I'm not implying you won't succeed. Hell, if the parlay payouts are true, and many are, you are dealing with the same probabilities as straight bets. The difference is that the larger the parlay the larger the drought between wins, but still the larger payout makes up for it.
It's a myth that parlays are somehow worse, just because it's a parlay.
Shit, the two pick parlay is one of the most dangerous weapons in a professional bettor's arsenal. I've made thousands upon thousands in my day.
What I'm saying is that the strategy to build the parlay is different if it's OPEN. You have a lot more choices if you keep it OPEN, for one thing.
I'm not saying OPEN is better, either, it just depends on your execution of what I always called "Parlay Construction."
The root of the differnce in strategies comes from the reality that the games are interrelated, including the results.
Many think the games are independant events, and you can bet that way, but it's simply not true for the broader markets.