Glad you and the students enjoyed building the kits! If you have any more feedback on them as you / the students use them more, be sure to let me know.
I will definitely consider changing the product documentation link to make it easier. It currently goes to a page where you just have to select the version of the kit to reach the actual instructions page. This was to help others who had purchased previous versions of the kit, so they wouldn't get linked to the wrong instructions.
Regarding import duties, I charge as close to cost as possible for shipping fees but sometimes (especially with larger value orders) you may be required to pay import duties (essentially, taxes and brokerage fees) to your local delivery carrier. Unfortunately these are out of my control as they're charged by the local government / carrier.