The 254 is one of the piston fillers of the 25x series from the 1950s. There is an earlier and a later version of the model, most reliably distinguished by the ink window: the early variant has a colourless, clear window, the later one a window tinted pale blue. On a black example the early version dates to roughly 1954 to 1956, the later one to 1957 to 1959. For other body colours the periods may differ.
The window variant is best judged on an empty, cleaned pen, since the tint cannot be made out while the pen is filled. The 25x models were solid everyday pens of their day and are no great rarity; they often turn up in estates. With a well-preserved nib and a sound piston mechanism they are entirely usable after an overhaul, which as a rule means a new seal and a clean-out of the feed.