It appears to be a scam with near mathematical certainty.
First off the math.
Im assuming 0 is not a valid number so high or low same 49.99% chance. (There are 4999 number from 50.02 to 100.00 inclusive, and 4999 number from 0.01 to 49.99)
So a win is double your money, and a lose gets you 10% back.
For a 1000 unit bet you get on average 2000*(.4999)+ 100*(.4999) = 1049.79 (this is your expected value, feel free to verify math)
OK, so were talking like blackjack odds if you're the house, you're guaranteed to win given sufficient bankroll and long enough time betting. (the house always wins, they can cover the loses the allow the casino to be open to bets long enough to let the variance (the ups and downs) cancel out)
So the next step is just to try it. So I got 1mil leaf and placed 10k bets as rapidly as i could. I should have kept track of all the numbers, didnt know you can only see 1 page worth of betting history. For the page I can see, I had 9 wins and 21 loses. Now you can flip a coin 100 times heads in a row, just whats the odds. So using a binomial probability calculator, there is a 99.1% chance one would have 9 or better wins given a 49.99% change to win and 30 trials.
Basically, yeah, its not provably fair, because it does not appear to be fair.
All in all i lost about 400k of the 1 mil (im not worried about the loss, it was a "fun" experiemnt, it was mined anyway, and you can never bet something you cant afford losing)
By looking at wallet transactions, I have 7 wins and 47 losses. Approx probability for these stats and the site be fair 0.0000000001
The odds of having that many losses given a near 50/50 is staggering to the point of plausibly impossible. So scam.
And really, what retards setup a betting scheme where they are mathematically going to lose 4.9%, its just a de facto faucet at that point.
tldr: Yes, it is a scam, do the math, try it, but please use minimum bet to convince yourself.
edit: CoinsFortress go F yourself for free! I looked at my wallet transactions and found that i bet 93 times and only have 7 win payments and 47 loss payments, so they owe me at least 40k leaf for the other 2 i know i won, just on the page i can see, and at least another 40k for the losses. So even if the rolls are fair (they are not) its still a scam since they cant even payout correctly.
My LEAF address in case I helped you not fall for this, or if lol CF wants to give me what they owe me lol.
fQG2amK5Vp6XvcFfy4aqGzWmg7T4NCuuFU