Mine has been great this year. Our old furnace (Yukon Klondike) had an electric plenum heater installed in it, which I moved over to the Kuuma early in November. Now that I have a backup heat source integrated into the system, I love the Kuuma considerably more. Previously I was having a little issue where the house would be a little chilly (like 66, terrible right?) In the early morning. I'd get up and put a load of wood in that would give us some heat to bring the house back where I wanted it, but then we'd get a bunch of solar gain when the sun got a little higher and the house would be 76+ degrees.
With the plenum heater, the house will stay 68 or 70 (whatever I want) overnight. The electric only kicks on a few times, but it's enough to avoid the dip. Then I don't need as big of a load in the morning, and I avoid cooking us out. The electricity for that heater is $.07/kwh, so the cost shouldn't be too bad. Also, since it uses the Kuuma's blower, and blows air past the wood furnace, it is just kinda giving a boost, but using preheated air.
I did see that
@JRHAWK9 modified his to have a variable speed blower instead of just a 2 speed, which would be cool, but beyond my current skill set. Maybe someday I'll tackle that.
One cool thing I discovered with the Kuuma is that if I load the thing 100% full at bedtime and leave the computer set to low, I can wake up in the morning and turn off the computer (shut the damper), push the coals back all the way, toss a little ash on top of the coals, and still have coals at bedtime 24 hours after adding wood the previous time.