Not quite true. Some of the MRI amplifiers I've worked on (including those built in the 1980s through the mid 2000s had switched power supplies for the filaments....
Wouldn't you agree, though, that within the scope of this thread, which is involved with the idea of an Amateur Radio Operator attempting to press an unknown design of a switcher from COTS availability for the task meets the criteria of what I posted earlier?
Too many unknowns that may crop up in that situation from my point of view.
Of course, Ham Radio has always been about experimentation and the breaking of paradigms that result from the hard work of a few individuals sharing their findings, wouldn't want to steer someone with the urge to experiment away from that sort of goal either.
At the end of the threads, each individual has got to evaluate their own situation and follow suit accordingly, the path that they desire, so there is no harm nor foul in just addressing whatever caveats one might conceive and then let that other person know what they might be in advance, is there?
Commercial Off The Shelf design would very likely be done by experienced engineers or at least a team led by such, coupled with the time, equipments and what all required to teast and proof the design before production commences. At least, that's the way these things *should* work <g>...
Also consider that the OP kind of referenced this particular situation as an "economy" move to avoid the cost of a much simpler solution, namely a simple power transformer....