Why not leave positive feedback and say something like "OK transaction, but slow delivery.". That gives other potential customers something to think about. I believe that every eBay transaction deserves feedback of some kind. That's what makes the system work, regardless of what some detractors of the system say on this bb.

Positive feedback doesn't have to be "praise", as eBay words it... just generally positive on the transaction.

I'll qualify my statement about "every transaction" by saying I give one feedback for each shipment of lots. See no need to repeat it if several lots go at once. eBay doesn't increment the positive counter more than once, and the one response seems to me to cover it.