I prefer to trade bitcoin on exchange because you pay extra charges to transfer the bitcoin to the store owner's wallet which means that you are paying extra for an item and very few stores accept bitcoin for payment. The fluctuation of the bitcoin price will also affect the price of things more often than usual.
I agree with you and paying extra is not a small value, what is not really profitable with that. So I think to that trade bitcoin on exchange is 100% better way.
but you need to choose which exchanges that you want because if you choose random exchange, you can pay a bigger fee for the transaction and it is better if you can compare about the fee for each exchange. it is difficult to find a complete store online that accept bitcoin for payment and maybe in the next years, we can easily to find the store online. but until that time is coming, we can use bitcoin for another purpose and we can save more bitcoin so we can directly use when the store online is ready.