It isn't safe at all - Bitcoin is like the normal stock market on steroids. It's already hard enough to accurately model and predict the share market (at least there are some obvious indicators based on company reports) but Bitcoin doesn't seem to follow any noticeable trend. It doesn't follow news - so far I don't think anyone has worked out what really affects its value aside from pure speculation. IMO, it's good as a side investment if you have a cash surplus but I wouldn't recommend putting my life savings into this.
Anyways who will someone likely to put all of it's saving in btc investment. Like any other investing scheme, invest only what can you afford to lose. Chances of making good output here is possible anyways but still one must have proper decision and a good backup just in case one goes wrong.