So I did the math for this game on Casinogrounds but I guess I can post it here as well 
This game is exclusive for LeoVegas as when this is posted but it’s only exclusive for a week or so I think.
So, onward to the math.
This should be the math for the average win of each freespin type, when we assume you get a win on each spin on average.
0 spins -> 0 (duh)
8 spins -> 34,66 times the money.
10 spins -> 52,95 times the money.
12 spins -> 75,09 times the money.
14 spins -> 101,08 times the money.
16 spins -> 130,93 times the money.
18 spins -> 164,62 times the money.
20 spins -> 202,17 times the money.
22 spins -> 243,56 times the money.
25 spins -> 312,87 times the money.
30 spins -> 447,66 times the money.
40 spins -> 789,41 times the money.
50 spins -> 1227,44 times the money.
And the gamble feature for the freespins math is,
And the % you need for each gamble for it to be +ev for the next step, this calculation is only to gamble ONE step, and not the potential of more gambles. The math is that either you win or you loose the gamble, so ((win median*0,5 – loose median*0,5) / collect median).
The 0% = that you should gamble it, you have nothing to loose (you can’t even collect on those so :))
8->10: 76,38%
10->12: 0%
12->14: 32,05%
14->16: 38,57%
16->18: 42.64%
18->20: 45.32%
20->22: 0%
22->25: 22,73%
25->30: 39,23%
30->40: 65.59%
40->50: 64,94%