Ya as far as I know 25Hz is still used in at least 2 of the major steel mills here in "Steeltown", and yes its for slow speed motor applications only..
On another note I just finished cleaning out my boss' storage barn and found a pile of old fixtures with similar ballasts inside, only difference was there was a screw to set frequency instead of that "plug" like the ballast I posted had.. Also in the pile of spare parts I came across an old oil burner and attached to the housing was a metal tag that said " This unit has been converted for 60 Hz operation".. Can tell that thing was around from the days of 25Hz power originally!
A.D
