It was designed as a single-purpose boat and I'll review it in that context. The mission is to go straight and paddle efficiently.
The hull is Swede form with plumb bow and stern, and no rocker. So, it optimizes speed for its dimensions. If you want a real speed burner, go longer and narrower.
There is no semblance of a keel molded in, so it does weathercock. It was meant for the pond, not open water, so no lost points here.
The knee pockets are very high, giving you the option of a racing position. Also makes it a little harder to J-lean or roll, should you want to avoid a wet exit and emptying all that water. However, a capsize is unlikely with its intended usage. Overall, the outfitting is pretty good. The construction is sturdy and of average build quality.
As far as I can tell, the only difference between this and the Cadence, its sister ship, is the deck height. If you can't find a Rhythm, try the Cadence, even though it was advertised for a smaller paddler. The deck is still high by normal standards.
The beam and hull design facilitate access to the water, even with high angle stroking. It's very enjoyable to paddle.
The listed weight is 42 lbs., which sounds about right. This makes it a nice little pocket rocket to toss onto the racks for a quick workout.
I'd guess it was discontinued because of insufficient market for a relatively short fitness boat checking out north of $1,500. This works to your advantage because you can find them used or on clearance very cheap.
If you're looking for a recreational boat or sea kayak, there are more suitable designs. But, if you enjoy paddling for the sake of paddling, this might be your ticket.