Before I chose the garn, I know the P&M had my interest. Compared to many of the other units, indeed, it seemed that the HX tuibing was directly accessible without much trouble. This is key I think. Many of the others require removal of panels, insulation, etc. just to get to them.
My primary concern was the relatively unknow/few reviews, and it is a huge investment. I felt more comfortable with the reputation of the Garn, the complete simplicity of the Garn, and have the integrated storage. Of course, the Garn requires a building....but I already had that waiting (after some retrofit).
As for water maintainence, it is true, twice a year I have to lift the manhole and dip in a little container. So far, each time, it has taken about 60 seconds. Not a problem. When I hear about many of the other issues, with nozzles, refractory, electronics, fans, idling, creosote, etc. it makes me really happy to know I don't have any of these issues. So far I've had no water issues, but only have had 3 samples. (0,6,12 months).
Though again, I repeat, if you need that hot water for the water to air HX, it isn't clear to me a Garn would be optimal. I just don't know how long storage would be able to supply water. 190-160 isn't a very big differential for that application. 190 is the generally accepted highest target temp for the Garn. Apparently the water chemistry starts to degrade more quickly after firing repeatedly over 190....That's the consensus anyways.