I have CS3.7s and before that I was using Thiel 7.2s. When I used the 7.2s, (many moons ago - I bought the 3.7s when they first came out - 2009?) someone was selling a lightly used 14BSST. I contacted Bryston before I bought the 14BSST as they made both a 15 amp and a 20 amp version, and the latter was made for speakers with lower impedances. I had a 20 amp circuit in the old house but they wired it (while the house was being built with 14 ga wire and so it basically was a 15 amp connection). I was concerned as I had a huge room in the old house with 19 foot ceilings which opened into other spaces. Bryston confirmed I should have no issues.
However, whem I got the amp, during certain music and movies (I have an integrated AV system), the protection would come on and the amp would shut down and I'd have to wait for it to cool. I sent the amp off to Bryston after contacting them (and as you indicated shipping is not cheap). It came back and they told me the amp worked fine and nothing was needed. I was not happy when the same things happended and so I ended up eventually selling the amp (and to temporarily use it, I built an amp stand with fans). I had gotten the 3.7s before I sold it. While it did not shut down, the 14BSST would get super hot (one would burn themselves touching the heat sinks).
So I ended up selling the 14BSST. I also had a (3 channel) 6BSST and I ended up using that for a bit in the old house. When I moved to the current house, about half the time the 6BSST (even though it was on its own 15 amp circuit - I have a total of 50 amps worth of circuits for the system, two 15 amp ones and a 20 amp one where I have my Torus RM-20 power conditior for my 2-channel stuff). So I ended up selling the 6BSST (and got another well reviewed class A A/B amp which drove the 3.7s a bit better). The arc fault circuit breakers (which I believe were adopted into code around 1998) were too finicky. Sometimes the circuit would shut down upon power up the 6BSST (on its own 15 amp circuit and nothing else on the circuit)
I also owned a 3BST (probably built a year before they moved to the SST series) which in my old house was used to power the front channels (Thiels SCS2s) of my master bedroom system for a bit and when I moved to the current house, I had it in a small bedroom (11' x 12'8") where I have a spare two channel system (which doesn't see tons of use). Anyway someone I knew asked me if I had tried Class D amps. I mentioned I had heard some at an audio show in 2015 and while they had gotten better, I did not think at that point I was impressed enough to give it a shot.
Fast forward a few years and I ended up trying a class D amp. I broke it in using my small secondary system where I had the Bryston 3BST. I always thought the speakers I was using at the time (Ohm Microwalsh Talls) were most of the limiting factor, I was wrong. I was shocked when I swapped out the Class D amp in place of the 3BST. Right out of box cold, it made the 3BST sound like entry level audio equipment. So I got rid of the 3BST, I've never heard the cubed series in an environment where I was familiar enough with the system and room (audio shows) to get a good enough demo to come to a conclusion.
So I always encourage people to try things for themselves as we all have different tastes and ears.