I agree, the P1 and the Ecos are very similar in performance, but the P1 PTB costs almost $2,000 less than the Ecos, so the price points are actually less comparable than the P1 and the Aquaprop.
What DPV makes more sense to an individual diver depends on what the major priority happens to be.
Price wise the Aquaprop sells for the same $2600 that the last of the Oceanic Mako DPVs sold for new over a decade ago. The Mako was 53 pounds (4 times heavier than the Aquaprop) but also had twice the thrust of the Aquaprop. Still the Aquaprop compares quite well in terms of over all cost/thrust/weight, and the Aquaprop does that by minimizing weight and initial cost - at the expense of thrust.
The Piranha P1 has twice as much thrust as the Aquaprop, and rather than 2 speeds, it can be programmed for up to 10 throttle settings based on percentage of maximum motor RPM (although 4 or 5 "gears" is more manageable and practical). The goal there was to give solid DPV performance and run time, but still keep the weight low enough to be travel friendly. However, the P1 still weighs almost twice as much as an Aquaprop at 24 pounds rather than 13 pounds. So if your absolute major priority is low weight (at the expense of performance then the Aquaprop wins hands down.
Price wise the P1 PTB can be had for $3915, compared to $2600, so the Aquaprop is only 2/3rds the cost of the P1 (not 1/2 the cost). However, that's just the initial cost. Three years down the track nearly all of the initial savings of the Aquaprop will be eaten up in the differences in battery replacement costs. $150 will get you a new set of four Enigitech power tool batteries for the P1, while a new battery/nose cone for an Aquaprop will set you back about $1000. Thus at 3 years out the cost difference between the P1 and Aquaprop is almost nothing.
Since cost after 3 years is a wash, it really comes down to weight. At 24 pounds the P1 is heavier, but also still readily portable so the question then is whether the hit in performance with the Aquaprop is worth the reduced weight. If you can live with 11 more pounds and $1300 more in up front costs (and no real difference after 3 years) you can get a P1 offering about the same performance as an Ecos.
It's worth noting here as well that a P1 PTB costs $2k less than an Ecos upfront - and you'll also save about $650 in relative battery replacement costs about 3 years out.
We looked hard at DEMA when deciding what to replace our Makos with and the P1 offered by far the most bang for the buck with the advantage of being small enough and light enough to still be travel friendly, and airline friendly with the airline legal power tool batteries. You've got to go with NiMh batteries in the Aquaprop to match that capability, even with the lighter weight.
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I ran some speed tests last weekend over a measured course at various rpm percentages in my CCR cave configuration and found that the P1 would produce:
230 fpm at 100%
204 fpm at 75%
185 fpm at 50%
165 fpm at 37.5%
148 fpm at 25%
At 150 fpm it's also producing a 150 min burn time.
