I've also had problems with river grass and ocean kelp using the Mirage Drive:
On the other hand, since I have no idea about the environment in which FLKayakAngler was making his comparison, I feel unqualified to comment on his statement. FLKA'a speed contrast sounded mostly reasonable and except for the PA sprint speed, was generally in line with what I found (and in conformance of another forum description for the Propel). His point on noise is on target and significant to fishermen. His preference of the Native seat confirmed one of the Native strong points. So I felt it was an honest enough comparison to present here.
Some additional comments regarding crank-driven props vs Mirage Drives:
Although having cycled for years, I've never been able to develop a good endurance with any of the commercial cycling props I've pedaled. On the road, momentum carries one through the uneven power cycle shown here (re: my reference to "dead spots" earlier in this topic):
With crank-driven props (including the Propel), thrust availability varies as above (no coasting momentum) so prop speed varies directly with power input like the sine wave shown here. Props are designed for certain parameters regarding RPM, boat speed and hull weight, so human powered props don't have the same efficiency potential as their motor driven counterparts.
The Mirage Drive operates similarly, but with a linear power application rather than rotational. A huge advantage is that the power peak stays on longer; a disadvantage is the reversal of motion as the pedals oscillate. IMO, the net effort works out in the Mirage Drive's favor, especially with optimal use of leg extension.
Furthermore, the Mirage Drive requires significantly less knee bending than the standard 17 cm pedals that are generally used. Leg power increases with extension, so more power can be applied to the Mirage Drive through its cycle. Knee problems increase with knee flexing and are not uncommon among road cyclists.
Most boat props have a fixed twist and pitch rate, giving rise to cavitation when operated outside their design envelopes. Hobie fins, on the other hand, are variable twist and pitch that can respond to changes in RPM, speed and weight. You may have noticed they don't cavitate.
Mirage Drives have other performance advantages that most props don't, including contra rotation and ground effect. The end result is that you can get more thrust, more efficiency and better endurance with less joint problems with the Mirage Drive than with cycle driven props. I have seen Turbofins beat custom performance props in an official race with similar length/width boats. In a test of virtually identical boats by the same indivual, Turbofins beat props by a significant margin in both top speed and one hour cruise times.
Personally, I have lots of hours driving a variety of cycle/prop boats and sold my Meyers Waterbike (by Seacycle) years ago when Turbofins came out. Prop drives do have some advantages despite their increased weight, size and complexity. Whether it's the desire for reverse gear or the nostalgia of having a prop-driven boat, they're nice to have around for those who want them. If I were looking for another prop system today I would seriously consider the Propel.