I recently bought a used 15' fiberglass Seda Gypsy that was equipped with a rudder. I waited to post a review until I put some miles on it. Yesterday I did 32 miles on the Huron River and was very pleased with how it handled on open water with 15mph winds as well as shallow rivers, and over small rapids. If I could rate the boat by feature it would look like this:
Weight: 4/5 Having taken the boat across 4 different portages in one day, you really appreciate the lighter weight. I'm 5' 10", average build, and I can pick the boat up and carry it (empty) over any portage. Fully loaded is another issue, I'd recommend keeping a kayak dolly in your rear hatch. Depends on how much you pack.
Tracking: 4/5 I'm not an expert paddler, but I find that the boat tracks very well over flat water, no rudder necessary. Over choppy and windy water, the rudder is recommended - with it, I had no issue tracking straight.
Stability: 4/5 Both primary and secondary stability are good for this V-shaped hull. As this is my first sea kayak, I have easily been able to adapt and handle this boat in any inland water conditions. I haven't tried taking it out on the ocean yet.
Storage: 4/5 The front and rear hatches provide plenty of storage for multi-day trips. I wish there was a day hatch as newer kayaks have, but I find there's some room behind the seat that works well for quick access items.
Maneuverability: 3/5 This is where the trade off comes in. In tight spaces on a river, navigating around downed trees was not easy. Edging + rudder + sweep strokes got me through but not after bumping into a few logs.
Speed: 4/5 Take my perspective with a grain of salt as I haven't tried other sea kayaks, but going from more flat bottom kayaks to this one, I saw a big step up in speed. I haven't calculated what the hull speed is, but on flat water with only moderate effort you can easily maintain 4 knots. On choppy open water with 10-15 mph winds, I could easily maintain 3 knots. To keep it at 5 knots (on flat water) requires a good deal of effort.
Robustness: 4/5 I've run it across some hidden rocks in fast shallow water. I've bumped it into submerged trees. I've pulled into shore a little too fast and run it across some pebbles and sand and haven't had any issues. I wouldn't recommend multiple rock scrapes, but my initial fears of a fiberglass boat and how it would handle with shallow rivers are mostly alleviated.
If you don't want to pay > $1500 for a new sea kayak, I would recommend a used Gypsy. After researching many different types of kayaks that people were selling, I'm very pleased with my selection. For those starting to get into sea/touring kayaks this would make a great boat to step up to. For those veteran kayakers, this boat will likely not meet a lot of their performance criteria.