The purpose of feedback is to let other customers know what to expect and if they should avoid a seller. So I wouldn't avoid leaving factual feedback, since to give incorrect feedback is lying and misleading other potential customers. You don't want that!
It might be worth contacting the seller, and very briefly stating that you were dissatisfied with the slow communication and long time for shipping. Don't mention anything about feedback, since that could be perceived as a threat. If the seller offers to reimburse you in some way, great! Your feedback can be "very slow communication & service; ordered on Sep XXX but only shipped on Oct XXX. Contacted seller and s/he reimbursed shipping." This is factual and lets customers know that there will be poor service, but that they can at least get the shipping/etc. sorted out if they request it. Of course, if the seller doesn't reply in a few days to your email, or replies with something like "oh, I was busy, sorry," then your feedback can instead end with "contacted seller about this but s/he made no effort to fix."
Keep in mind the other customers, since that's what feedback is about. Give the seller a chance to make things right, but don't demand anything, and keep your subsequent feedback factual.