What is this cartridge fuse style component?

It is an electrochemical hour meter, historically a thin tube filled with mercury with a drop of an electrolyte, current flowing causes ions of mercury to be transported across the electrolyte moving the bubble of electrolyte along the scale.

It almost certainly still works just fine, but will gradually move back the other way if fitted in reverse....

You don't see them much anymore, counters in non volatile RAM being cheaper and more convenient.

The text beside the mounting clips says "X 200 Hour", so I'd guess that it records operating time of the tape player.