I might be wrong, but IMO any investment has its disadvantages and therefore it comes with risks. For me, just as like for most people, the main disadvantage of bitcoin is its instability. But it also may serve as an advantage, coz it also make btc profitable. Anyway, its never about absence of disadvantages, but more like about prevalence of advantages.
I agree with you, the instability in the price of Bitcoin can be regarded as one of the advantages of Bitcoin, because due to the frequent and sharp change in its price, it becomes possible to constantly earn. But this is if we consider Bitcoin in terms of trading it, but if we regard it as a means of payment, then for many such price jumps are a tangible disadvantage.