I assume you meant Mountain Duck (https://mountainduck.io/).
I’m mildly familiar with it as it was the most serious contender (on paper) if I ever needed something more than the built-in OS support.
It is by the Cyberduck folks and shares the same backend library (and supports mounting). It’s actively developed (with quality changelogs - yay - Changelog) and free of advertisements.
It is a paid product (albeit relatively affordable - although I realize affordability is locale specific and I’m not sure if they have pricing for different markets). The backend is open source: GitHub - iterate-ch/cyberduck: Cyberduck is a libre FTP, SFTP, WebDAV, Amazon S3, Backblaze B2, Microsoft Azure & OneDrive and OpenStack Swift file transfer client for Mac and Windows. if that’s important to you.
That said, both of the ones you mentioned appear to have evaluations. Have you tried them out?