First off, I live in Colorado.
And Like you, I have been dealing with geothermal for a LONG time.
Why? Because it is very efficient and cheap to run. However, I have heard of these costing up to $50,000 in the Denver Basin. Namely in the city here in small yards/large house. And yes, we have California style building here.
Dandilions approach is not the small size, but the way that they drill it. They spent a lot of time trying to come up with a cheap way to drill. It appears that they combined drilling with impact. IOW, they are focused on the drilling.
Now, geo-thermal HVAC is all about moving heat between the ground to the house. Generally, dirt is an insulator. Some of it, such as clay, conducts heat nicely. As such, most companies have different strategies on how to do this. Some will dig trenches 3-4 meters down and then lay horizontal piping. Ok if you have a large yard. Others will drop a couple of pipes into ground water and then open loop it from there (horrible idea; raises water temp and encourages growth). Then the closed loop wells involve 2 different approachs; dig multiple wells(2-10 of these) down to say 300' OR dig just 2 wells DEEP;
Starting new wells is actually expensive. As such, dandi has apparently chosen to limit the wells to 2 of them and simply dig deeper/faster.
You mention about the heat pumps, and basically imply that these are bad. The answer it that these are needed to actually shift heat. For example, here in the west, pulling 55F out of the ground does not heat a house up to 68/72F. Far too many of the cheap ones go out. So, you need DECENT ones. Dandilion will apparently use water furnace 5 series, which several of them are well known for good service. Neither cheap,nor expensive. But once geo-thermal really starts moving foward, bet on it that these HPs will drop in price.
BUT, the real issue is that the local contractors really stick it to the retrofits. HORRIBLE prices. I mean horrible. They talk 30-50K in this region. That is just plain crazy. I will say that adding geothermal while constructing a new home is the right way to go, but, few builders do it. Oddly, it can be done for about 15K, even down to 10K, depending on the situation.
Now,if these dandi can do it at 20-25K ALWAYS, then they are doing great and will make major changes to America. COmbined with a small solar set-up, and some decent insulation on a home, this is IDEAL.