They are still cool. I just recently installed one :)
The vacuum tube ones are IMHO the best, but there are also ones that circulate a heat exchange fluid in panels for direct connection to a heat-pump. The advantage of the latter is that you get good efficiency out of them in the winter, but it also means that the heat-pump has to run all the time. My vacuum tubes work fine most of the year with only a small circulation pump running (and smaller systems with a thermo-siphon don’t even need that).
What did you end up spending for it? Are you using it paired with an existing hot water heater?
It’s combined with a stand alone air-to-water heat-pump that shares a hot water storage container with the solar thermal panels. Prices are hard to compare and I actually got a small government subsidy for it as well, but the solar thermal vacuum tubes alone should be less than $500 for a typical family home.
Due to economics, using photovoltaic solar panels and an electrical heater is actually cheaper. Which is a bit stupid of course. I think water heater are more compact but more expensive. And they need a pump and a heat pump and more maintenance with moving parts and antifreeze etc.
We have one, it works reliably for many years, even in winter when there is sun - problem is sunny days are too rare here from Nov to Jan. If you get one, get a big tank, and optimise setup for winter (low sun angle), more than enough hot water in summer.
I have tried to think about the feasibility in installing a solar water heater on a monolithic dome styled house.
