@Thebomber I’m a big fan of my heavily modified single boiler for just the reasons you list. Rock solid temperature stability, small footprint, easy to descale (I’m in Oxfordshire and also use Brita filtered water), energy efficient (as to steam you’re only heating 300ml from brew temp to steam temp, not a large steam boiler from cold).
It’s a bit of a hassle if I’m doing more than 3 flat whites (as I can steam that much milk in one go), but that happens rarely enough that I’m happy with the compromise.
For making one coffee (my normal use), I’m not convinced it’s that much slower. I pull the shot first, and by the time I’ve cleaned the portafilter and weighed out the milk it’s up to temp for steaming.