I've got two St. Croix stoves, good choice! The first one I hooked up with Simpson Duravent and the second, Selkirk. In the end, both worked fine. The Selkirk was a little easier to install but I don't like the clean out tee as much as the Duravent. Duravent thimble is better looking. Overall the Selkirk quality, the fitment mostly, is a little better.
If I had to to a third, I'd buy which ever is cheapest.
One differentiator is the clearance to combustibles, iirc the Selkirk can be closer. If you're feeding it through a tight spot that may matter.
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