The efficiency of a Zehnder is certainly worth it over most American ERV/HRVs. They have efficiencies in the high 80s to nearly 90 percent. Look at the HVI listings and sort by highest Max Rated Sensible Recovery Efficiency: https://www.hvi.org/hvi-certified-products-directory/section-iii-hrv-erv-directory-listing/107
You don't have to use the Zehnder ducting if you are going to pay an contractor to install it. You can use rigid metal ductwork to bring the costs down. The flexible comfotube makes install easier, especially for DIY, since you don't have to put together metal ductwork and seal it, and you only have to drill 3" holes where the tubes need to go through framing.