yet people are complaining that it has been a bad investment
I think that is because in the long run, people tends to be used in the fast changing price of Bitcoin and that is not dumping but they are used to pumping. Since the price are changing fast, they always think that it will always be a pump and they are scared of the dump. They are complaining since they are scared of what may happen in their investment.
I do admit bitcoin investment is very promising, but you still must be able to accept any risks that occur such as instability and the security of your account that at any time can be stolen by others, not just bitcoin there are many other currencies that are good for long term investment.