Okay, so I took the plunge and ordered with Musik-Productive, with prices listed as including Tax and Custom Fees.
Confirmation email received, and itemised on it is a separate figure (within the total) for “Import Duties”. So, it looks like they’re right, and they’re using UPS as a customs broker?
Proof is in the pudding (whether I get a bill from UPS or not), we’ll see!