4iiii will install a right side PM on your Ultegra or Dura-Ace crank. Or is your crank something else? Most all their left side PM's that I'm aware of will work with an added right side 4iiii PM to give you a dual sided PM.

While tariffs could be issue since they are in Canada. A header at the top of their page suggests they are priced currently with them covering the tariff and brokering fees. So maybe that makes their prices look higher compared to others selling from outside the US that are leaving those fees and tariffs to the importer of record. Though if you are pricing from a US based vendor, then the Assioma's have already had their tariff and fees paid.