The 908 is the "Value Line" version of the 3913/3914. There were two variations, the 908 and the 908s. The "s" was the stainless version.
Both are very reliable semi automatics. There were changes made to the 3913 design to reduce production costs.
All accessories and many parts of the 3913/3914 guns are interchangeable with the 908 and 908s.