That is right - using bitcoin to buy for just small things are quite not that wise because the price of bitcoin has really a good potential of increasing its price as time goes by. It is just really good for investment I think.
Yes, Bitcoin is not good for buying small things. But that's not because the price fluctuates. It's because the entire structure of the crypto (in it's current form) is not scalable. The current transaction fee for BTC is $25... that's absurd for buying anything less than about $1000. And that high transaction fee is a direct result of the network being overloaded.