I don't think the buyers will be confused at all... they'll see the drop-down for quantity and if they want to order more than one, they can very easily.
And as far as thinking it's costing more, it's not costing any more than if an item sells and you relist it for 20 cents... at least this way it's going to auto renew and you won't have to monitor your listings.
If something sells in the middle of the night while you're sleeping, it's back to the front of the line and available to the next buyer who might have wanted it, but with the old system, would have seen that the item sold. In the unlikely event that they'd convo you for another, they'd have to wait til you logged in to see the convo and renew it for them, when in the meantime, they might have decided to find it or something similar elsewhere.
My items are mostly ooak, so I don't list multiples of many items, altho I may do so with my handmade findings, and I've actually had buyers convo asking when I'll be making more, or if I could set up a custom order, since it sold... so in addition to being a time-saver for myself and the buyer, it may even score me added sales too :)