I built an SC-1 at Cape Falcon in summer 2007 - it's the design precursor to the F-1, and is an authorized skin-on-frame version of the Mariner Coaster. The F-1 is quite similar, although it has been further optimized for better behavior while surfing, and may be a bit faster, and is a bit narrower. From what I've read over at Qajaq USA, the boats behave very much the same. You could also read reviews of the Coaster for more feedback.
After paddling the SC-1 for three seasons, it is still my favorite boat. It is short, but not slow. The maneuverability is good, as you would expect - the skeg profile of the stern aids straight-line tracking while the pronounced chines (from the cockpit aft) allow the boat to carve lean turns fairly automatically. The forward part of the hull is narrow and Swede-form below the waterline, in spite of the blunt appearance of the bow. The wetted surface area is very low, so overall, the drag is surprisingly low - glide is impressive to everyone who has paddled it. I've loaned the boat to many people, and in particular women find the boat comfortable and easy to drive. I am not small, however, and I like it fine. I believe Brian tailors the F-1 to the paddler, which is a bonus.
My boat is 13'9" with a beam of about 23.5", and is quite stable at rest. For whatever reason, the boat is also comfortable in confused seas. This is the real merit of this boat for me, as I paddle in L.I. Sound and the Hudson, both of which are prone to swirling currents and really big boat wakes.
The max width occurs behind the cockpit so the hull does not really interfere with the paddle stroke, unusual for a short boat. The peaked fore deck is pretty high, which is nice for shedding waves and gives some space up front. The steep angle of the deck keeps the sheer away from your knuckles.
For me, the front of the cockpit is a little low and I may modify it someday. Some of my problem may be my seat - I have bought a new seat (Bumfortable), but it's not installed yet. However, I am an anomaly - most people with a sea kayak background find the cockpit roomy and prefer the normal pad seat.
In the end, I think the only thing you give up in a boat like this is some top-end speed. For me, this is not an issue, as I have little ambition to go fast. If I do, I paddle my Struer. Brian is a very talented designer, and the F-1 represents a significant amount of experience and experimentation to generate an advanced hull. The fact that it is hand-made may hide that to a certain extent, but don't be fooled. This boat is being made and enjoyed all over the world by better kayakers than me. In my opinion, it is the perfect answer to those who think a capable sea kayak has to be at least 17' long - it just isn't true.
Finally, no one should be dismayed by SOF construction, it is quite tough. Get a set of Spirit Line float bags and you'll be fine. I've paddled myself at flank speed up onto a rock in the middle of a reservoir in NJ, and had to knuckle-walk myself off. I only scratched the finish - no tears. Oyster shells haven't been a problem, but I'm careful around them. The only thing that scares me is hidden rebar at the shoreline, but that could hole a glass boat, for that matter. I give this boat a 10 out of 10 because it's everything it claims to be, plus I made it myself and why wouldn't I like it?