The most annoying thing about slots that don't have a buy freespin feature is that when our luck is bad, we can spin hundreds of times but not get a single free spin bonus. It's such a waste of time and money. In slot games what we are waiting for is a free spin bonus, if we don't get it, it will be very annoying. If there is a buy freespin feature, then when we have spin normal several times and the spin looks bad we can buy freespins and we can immediately enjoy the sensation of freespins. But if our account is not having luck, buying freespins often makes the balance run out very quickly.
In fact there are even some slots without free spins round so it will be impossible to add bonus buy in such slot. However I have to agree that it will be annoying when we have made many spins without free spins or bonus round but it is also annoying when we get many free spins but the result are bad. In a situation when I have made few tens spins but the result is not good, I will not even buy the bonus because I believe the result will also not good. Most other gamblers say that the slot is in the cold time, so anytime I feel that the result is not that good after few tens spins, I will prefer to move to other slots than buying the bonus round.