I would say it is potentially worthwhile as a speed control technology, just not important and no longer significantly beneficial. Now that the 60Hz coming out of the wall in the US is dead-accurate for this, devices using the mains frequency for clocks perform a lot better than 40 years ago;1970s servo speed controllers can perform better today than they could back when they were made.
Just meant it's only that, doesn't relate to the quality of the rest of the system.