Product review (4 stars): Good Product, but lacking a complete solution
As a vent cap, this is a very good product.  It is not flimsy or poorly made, and the color matches the roof perfectly.  Other products are metallic in color and stick out on the roof like a sore thumb.

This vent is designed with rigid vent tubing in mind, as with a range vent.  My application was for a bathroom vent.  The old ventilator was much too noisy, so I decided to replace it.  I found that the flexible vent, made of plastic, was pockmarked with tiny holes.  I wanted to use flexible metal vent tubing that would last a while.

There is no provision for a vent that is not self-supporting in this cap.  It merely fits over the end of the projecting vent on the roof, and does not "capture" or support it.  My solution was to rivet several angle brackets onto a 6" piece of 4" vent tubing and attach it to the underside of the roof.  Then I fit and clamped the flexible tubing to the underroof end of this.  So, the flexible tubing was supported and held in place, and the vent cap fit over the end of the upper end of the rigid tubing.

Not a significant problem, but something you need to be aware of if you purchase this.