In 1974 the FMI 80 was a very good low-priced speaker, better than many much more expensive models from other companies.I went from Altec horns to FMI 80s (Fulton was here in Minnesota). Eventually I had a set of Js and then Premiers, before going in a different direction.
But that set of 80s I had are still alive- doing background music duty at a coffee shop in NE Minneapolis.
In the 90s we sought out some SET amps, since they were a sort of rising star back then, to see if there was anything we needed to be worried about. There wasn't. Class D- same thing, until just very recently. I've been of the opinion that class D was the rising star in amplification for some time, but that they just weren't fully realized.
All technologies follow a price/performance curve, with lots of investment initially with little performance gain. As the technology gets sorted out, big gains are made with little money so the tech improves rapidly during that time. When its mature, only small gains are made and with significant investment.
IMO only, we are somewhere in the middle to top of that curve; I don't think that class D technology is all that mature yet. The reason is that relatively small players like Merrill are able to make contributions that advance the art. Heck, we've even been able to do that. So I have to assume its still got a ways to go. At any rate, recent Class D amps are sounding a lot better than even just 5 years ago.