It's quite amazing if they can say SS retain heat better than brass.
Conductivity
Brass – 109 (not 159)
Stainless Steel – 16
https://en.wikipedia.org/wiki/List_of_thermal_conductivities
Even stainless steel boilers are a very bad idea.
Do they clad layers of copper in it?
Looking at how thin is it, don't think so.
In the video, when you insert the below piece to make it a double/single portafilter.
There's a silicon holding gasket. Silicon has poor conductivity and creates another barrier to transfer heat to the underlying piece
If that nozzle is not heated well enough, i think it plays quite a big part to the end result as the cool SS will cool your extraction.
Cafe switch their machine on the whole day and the portafilters are always heated and for a long time. So they are more likely to be heated well enough, for home won't do unless you on the whole day.
However, if it's a high traffic, i have doubts that SS portafilter can retain the heat though.
For the bottomless, the coffee normally gets into contact onto just the basket then go straight out. Don't see how will it touch the holder much, so don't see any major issues with that.
In Italy, they been using such chrome plated brass portafilter like forever, much longer than Americans by multiplications.
Mine haven't chipped after using for few years of use.
Over a long time, SS can rust too.
I dunk my portafilters to my used grouphead detergent and they are clean like new after a spa.
I won't consider to buy that at all, but you can try and let us know
