Rudders or skegs are great on flat water. If someone is going to do any river paddling (and, again this has to do with which rivers and where), you don’t typically use a rudder or take a boat made of anything but plastic. There are usually too many places where the bottom gets scraped on rocks or gravel (or logs). A sea kayak is typically way too long for paddling on a river, particularly if there are a lot of hairpin turns. There are a few rivers I have paddled in Michigan that even a 12’ boat was too long.
I noticed that Potomac kayaks are sold exclusively at Dick’s sporting goods. I would just tell you that I have been to a number of different Dick’s stores in the past and have never talked to anyone there who knew the first thing about kayaking. They seem to take sketchy canoeing experience and assert that it applies to kayaking (sometimes it does and sometimes it doesn’t).
The description of the material used to make Potomac boats is a proprietary material and sounds very similar to the material used in Hurricane kayaks. I have a larger friend (under 250) who split the kayak where the colored deck joins the white keel because it really wasn’t designed for a larger paddler.
Potomac is actually made by Pelican.
If you would be comfortable pm-ing me your general location (nearest big city), I can see what reputable boat dealers are offering demo days in the next few weeks so you can actually paddle several boats to compare. An alternative is to look up local (near you) canoe liveries and call a few to see who puts kayaks out on the water for customers. Get out on the water and paddle a few boats before you commit to one based on what a Dick’s clerk recommends!