I've used the KayakPro SpeedStroke GYM for about three months.
First, the pre-buying experience was outstanding. I had some questions, so I E-Mailed them in. Grayson Bourne, the company founder (and World Champion and 5X Olympian), promptly called me to answer all my questions personally.
I found it straightforward to assemble.
Using the machine is amazing. I find that I am getting better cardiovascular workouts than anything else I've ever tried. I've found that both my technique and strength are improving (in addition to my cardio fitness level). The built-in HR monitor receiver & display is a nice touch. The console display is simple and useful.
I had a slight problem with the original console -- it had some kind of partial short that drained the batteries quickly. Once I informed the company, they immediately sent a replacement.
The customer service has been completely above reproach. This thing appears built to last forever.
I haven't used any other kayak ergometers, but I did notice that this one is longer than any others generally available (e.g., the PaddleOne K, the Vasa Kayak Ergometer, the WEBA Sport Kayak Ergometer, the Vermont Waterways Kayak Adapter to the Concept 2 Indoor Rower). I'm told by those who appear to know that it is vitally important that the rope go to as forward a point as possible -- otherwise, the catch (and/or the return) is quite a bit different on the erg than on the water.
My only real complaint about the GYM is that the footplate kind of hurts my heel while paddling. It isn't really too bad -- I've kind of gotten used to it. But this is one of the VERY few things about this machine that could use improvement, in my opinion.
I have no reservations whatever recommending this machine. The cost may seem a bit high, compared to some others, but if you compare the cost of this to a good surfski, they are about the same. Here in the midwest, you can only use a surfski perhaps seven months a year. For the rest of the year, this thing is going to be keeping you in shape and helping you train for your next in-water session. You might even use it sparingly during the summer (it is much more convenient to get a quick workout in in your basement than to put a rack on the car, load the boat, travel to the put-in, and do the reverse after your paddle).