Finally, let's take a brief look at differences between "OM-1" and "M-1".
They look almost the same at a glance.

The differences between them are product's name engraved on the top cover, and the lens-system name (OM-SYSTEM and M-SYSTEM) on the lens front.
The M-1 is now a rare and a collector's item, for not so many was manufactured.

Well, this is about it for OM-1.