If you take a 40X wager bonus then you are insane. I wouldn't dare touch it. There are plenty of casinos with 20X - 30X. What FJ is doing is ripping people off, and some of you just continue to kiss up to them. 40X is roguish
But, I believe people who think x40 is a must on a horrible odd bet are not really well informed about how x40 works. You can play with 1% of your bankroll and keep on betting the smallest wager there is and actually bet on 90% win odds as well and keep doing that on auto forever until it reaches to x40.
The possibility to actually lose all of your money in that scenario is very little and you will most likely get the deposit bonus. You don't need to play x40 at once and get it, you can play anything, there is no restriction on your bets, you just have to wager x40 in total. So, if you deposit 0.5 and the x40 is 20 btc that means you can bet 10 satoshi on 90% for 200 million times, even tough you may lose a lot in there you will most probably not lose too much and will get that bonus after all.
Sorry but I'm not here to support Lucky7btc but I just want give you the truth. You are saying about wagering on 90% win chance, means that you are referring to dice game or maybe other similar game while in fact only Slots game are counted 100% towards wagering requirement. I'm not really sure about dice, but as I know wagering on dice is not counted towards wagering requirement. So your scenario wont work to complete the wagering requirement. One more important thing is that "only bets using the bonus money will be counted towards wagering requirement", means that you need to lose your initial deposit first before starting to wager for the requirement.
I know 40x wagering requirement on deposit bonus is a standard rules in this gambling business, as most other sites also has the same rules. So it is players own decision whether to take the bonus or not, as the site is not forcing players to take it. Overall, it is just an offer from the casino. Players may take it or ignore it. Simple as that.