Regarding power draw, would a gyro use any more power than Wesmars, ABTs or Naids? The PTO power takeoff driving a hydraulic pump is not free energy. With a 4KW or so "generator" driven off an engine when cruising, the genset use could be negated.
It all comes down to cost though, in a new build the gyro may have some real economic attraction with operating cost savings when cruising in the 12 to 18 knot range. I'd guess the target audience to be non trawler designs where stabilizers are not easily fit due to hull shape.
It's very true that both consume power, and let's assume for argument's sake that both consume the same amount.
At least in my case it was about where/how you get the power. While underway the main is obviously running, and adding a hydraulic pump to drive a fin system is relatively straight forward and cost effective.
Electricity for a gyro would need to come from a good sized electric source. The cheapest would be your genset, assuming you don't mind running it all the time you are underway, and that it has sufficient capacity. Under many situations, this would be the ONLY reason to run the gen, and hence becomes objectionable. If you run your gen anyway, then it's not a big deal.
An alternate source would be some sort of enlarged main engine driven alternator. Perhaps a hydraulic generator, or a beefed up DC alternator and inverter system. All are possible, with varying levels of cost and complexity.
The space thing is tough to get around. Provided you have an accessible and suitable location for the actuators for a fin system, the in-boat foot print is pretty small. But in boats under 45' or so I suspect finding a suitable location will be very difficult. The gyro's a big box. On my boat it would have completely consumed the laz. As the boat gets bigger, at some point you need two gyros, but I don't know where the break point is.
Trade-off, trade-off, trade-off. That's what makes it all so interesting.....