The Ultimate FX 15 Tandem is a vast improvement over the previous Ultimate 14 tandem. The seats are easily adjusted to high or low position. The initial and secondary stability is excellent. I only paddled this tandem so I can't comment on the solo configuration, but for tandem there was more room for the front passenger than in the older model. Also the seats now sit in a pan that can easily be moved.
My old Ultimate 14 tandem was hard to adjust the seats and they had to be blocked up with foam bricks. The FX is more user friendly from the new seats to the groove track accessory tracks and the improved yokes, there are a lot of places to store gear and add accessories.
This is an excellent kayak for someone who is looking for the roominess of a canoe but the stability of a kayak.