I have no idea if its a scam or not.
It seems like they are using your investment to invest in JUA's mining operation, and they estimate a 10% yearly return.
You can opt in or out at any time, and you can withdraw at any time, so I am not sure what the downside is supposed to be, unless the downside is that if too many people all suddenly withdraw at once, bter all of the sudden goes "oh crap, we lent some of your BTC to JUA, we cannot cover all our withdrawals right now, so if you opted in you have to wait".
10% yearly is an offer that is reasoanble to make if you have a good investment opportunity (and they didnt even promise 10%, they just 'estimated' it), so its not in obvious scam territory. I don't know what the risks actually are because they didnt really give details. So, beware if you want to participate, but it is possible that its legit. I would guess that if JUA does well and makes money then you're going to get a decent return, and if JUA fails or loses money, or everyone tries to withdraw all BTC from bter at once, then I have no idea what is going to happen but you might be at risk.
I already took everything out of bter so I have no skin in the game.