I have owned my Capella 166 RM for about a month, and I've paddled it about 75 miles during 10 outings so far. My outfitter let me demo it over a weekend, and I decided to keep it since it paddled so nice.
Initial stability is less than my first kayak (Necky Manitou 13), and I tipped over the first time I climbed in the Capella. Fortunately I haven't repeated that gaffe, and the secondary stability is excellent. The Capella tracks very nice even with the skeg retracted, but the skeg is great when paddling in certain winds. It is easy to edge and turns well. It also handles very well in rough water and waves, and I actually seek out boat wakes when I'm paddling it because it's so fun.
The Capella has tons of storage space and would be suitable for touring. It has 3 separate hatches and bulkheads, which is a great safety feature as well as providing storage. The hatch covers are easy to use and seal great. The kayak also has plenty of riggings.
The P&H seat, for me, is it's strongest point. It provides plenty of support and is very comfortable. I paddled my Capella 16 miles over 5 hours the second day I had it, and my rear was never uncomfortable. In my Manitou, I would have been squirming after the first hour or so.
The Capella RM is not particularly fast, if that is important to you. My average speed in the 16'7" Capella is barely faster than my 13' Manitou, although it's easier to maintain a faster pace over long periods.
My Capella is the light blue color (sort of a Robin's egg blue) and it discolors easily. Mine quickly developed marks on the hull where it rests on my Yakima rack, and it also stains easily in dirty water. The marks are not easy to clean off. However, the top portion (above water) of the hull still looks like new.
The Corelite plastic used in the Capella's hull has relatively rough finish, which may slow its speed. The roughness also prevents suction devices (such as LED lights) from attaching well to the hull.
Overall I am very pleased with my Capella, despite the shortcomings. I also paddled the P&H Scorpio and liked it even more (felt much quicker) but couldn't justify the additional cost. My Capella was on sale for $1,000 new, and the Scorpio would have cost nearly twice as much ($800-900 more).
The quality of construction and attention to detail is great on my Capella. I have also heard very good reports on their customer service and warranty protection.
The Manitou is fast for a boat its size and tracks very well. I never have any trouble paddling it straight, and I'm a newbie. It is also very stable and I've never come close to tipping it over. The seat is very comfortable, although I sometime get a little sore on longer paddles, possibly due to bad positioning on my part. The Manitou has plenty of shock cords to lashing things down and a rear hatch, but a small hatch in the front would be really nice for storing day-use stuff. It's also a nice looking boat with graceful lines like a British sea kayak, and I love the Fire (yellow-orange-red) fade of mine. The Manitou is also very light (45 lbs.) for a poly boat of its size and easy to load on a rack.
I don't have any strong dislikes, but quickly regretted not buying the Manitou 14, which is slightly longer and has a front bulkhead and hatch. I have paddled the 14 and it performs almost identical to my 13, but the front hatch/bulkhead is an important feature for sea kayaking that I was ignorant about when I bought my 13. The 14 is also a little more buoyant and faster for someone my size, 5'11" and 190 lbs. However it is less maneuverable than the 13. The 14 also has a skeg, which frankly I don't think would be needed very often since the Manitou tracks so well without it.
I was initially considering the Capella for my next step up in a sea kayak (currently paddle a Necky Manitou 13), but I might have to save a little longer and get a Scorpio. The Capella was my clear second choice among the kayaks I paddled, but the Scorpio was tops. Oh yeah, both of the P&H kayaks were poly models not composite or fiberglass.