I think Bitcoins saving is quite risky, because compared to other forms of investment such as gold or dollars, cryptocurrency is more risky because the possibility being hacked is so high, we could be stolen bitcoin or the ability the network system attacked, you lost all bitcoin in the second. In addition,fluctuations in bitcoin price are highly impacted by the market so investment in bitcoin is unsafe solution. 
Agreed bitcoin too risk to hold as saving but just about it price not because hacker etc. Due you can hold it in cold wallet which safe enough for you to hold it forever with risk in this way. The risk in my opinion as you said just because it value easy to evaporate. So about this bitcoin is unsafe as long term investment for me.
BTW, I only invest in real estate as well
