It's a bonus more similar to bonuses on various other casinos where there's a wagering requirement (it's not just free money). If you want to play Hi-Lo, it might be worth taking if you were going to wager near the rollover amount anyway, but it is a -EV bonus (25x rollover with a 5% house edge) and you're expected to lose 25% of your stake.
Completely right.
Here I give an example to make it more clear.
I claim 1000 Satoshis. 1000 Satoshis will be deducted from my balance and I will have 2000 Satoshis on my bonus account.
If I play HI/LO game and I wager 1 Satoshi 1000 times, the house edge guarantee that I will lose 50 Satoshis. (In long term, it is 100% true and that's why I considered the amount of each bet only 1 Sathoshi).
To become eligible to withdraw my balance from my bonus account, I have to wager 1000*25= 25,000 Satoshi. So, I will lose 1250 Satoshis. So, I become eligible to send the entire balance from my bonus account to main account when I have only 750 Satoshis.