Sorry I can't offer direct comparative experience either....never seen the Vertex in person.
Personally I would discount the Vertex on account of its shape, size:footprint ratio and cost. Aside from this skimmer, the company is known more for sponsoring Chinese knock-offs of Euro-Reef's skimmers so that gives me further reason to discount them.
IMO, pick up the Reef Dynamics that makes the most sense based on either size, fit or cost...whichever is most important to you. Bigger would be better in several ways, but smaller would definitely still get the job done and also have its benefits. They are made here in the USA by a company that has always (even back when they were Euro-Reef) made great skimmers, and which still supports local fish stores. YOUR local fish store, in fact. :)
-Matt
Thank you Matt!