I would always recommend the brine heat pump if it is allowed: The additional costs are manageable today (it was quite different 20 years ago).
No offense, but the statement is simply wrong in such a generalization. The brine heat pump stands and falls with the development of the heat source and its costs. These are, for example, very different regionally for a deep borehole. About half a year ago, I posted my offer for the drilling here in Franconia. The drilling was about 15k. The heat pump itself, i.e., the unit, is comparable, but not the development. And from the 15k, you can deduct the 5k subsidy if you want, leaving you with 10k additional costs that do not amortize nearly as quickly. Regarding the regeneration capacity: the ground apparently regenerates through precipitation and moisture – that's how a geologist once explained it to us. So if the soil can hardly absorb precipitation (clay) and/or it rarely rains, it can become problematic. This has already become an issue for a few builders of our architectural firm. They insisted on a brine-water heat pump despite warnings and are now struggling because under the mentioned circumstances, not enough energy can be extracted from the ground. Not to be misunderstood now: I would also always rely on a brine-water heat pump if it would reasonably pay off here and the conditions were right. Unfortunately, they are not. But the idea that the brine-water heat pump is a universal tool and always works everywhere is simply not correct, and I want to raise awareness for that. In most cases, however, it should be a good solution if the additional costs for the drilling are within limits. And again, the local situation plays a role here. Can you get by with one borehole because you are allowed to go deep enough? Or do you have to fraction, for example, drill 4 or even 6 boreholes, which is significantly more expensive.