IMO only invest the amount you are willing to lose as BTC has proven to be a very risky and volatile investment, particularly if you have no intention in holding for a very long period of time,
Just yesterday, the price fell to around $2100 which means $900 loss per BTC if you bought at the highest peak, but it recovered today, that alone shows how volatile it is as an investment.
Right now the bitcoin users are very strong in bitcoin and they are taking every dump as an opurtunity to buy in low and that you can see in latest dump when the market started to dump but still the users bought and today price back 50% up. So i dont think that investing in bitcoin is bad choice and about risk their will always be risky in any investment because no one can give you 100% unrisky investment option.
Bitcoin investment well no investment is a safe investment
There is always a small amount of risk in every business
Bitcoin investment is a good investment for a long time period as it will definitely grow , but it is not the same if we look day to day
The values are always fluctuating so if some one goes for short term investment they may end up in loss
But those with right trading skills an Technics can make profits
They evaluate the fluctuating graph carefully and then buy at the right moment to make profit , while the one who buys btc on the higher mark ends up in a loss ,we can just make Bitcoin investment safe by using trading skills but certainly it has some risk