Not sure a 6" diameter gauge could ever be called subtle......... thinking temp gauge for woodburner output, another one for thermal store and pressure gauge somewhere (or maybe 2- one for the woodburner and one for the thermal store). Nice row of 3 (4) in lovingly polished brassMy sister will so slap me when she sees the finished setup (she's more of a minimalist)
With a solid fuel heat source and a minimalist look they will work really well as they add a subtle feature and also perform a valuable function.
I fail to see your problem? Tell the sister it's regulations and that's how they have to be done!!
Jon