It looks like that is an early Powermate Jr, and just like the Sidekick on the Electrolux. We have a 1999 Whispertone canister with a similar PM Jr, but it did not have the reset button on it. There was also another PM Jr that had the same innards but the cover was more rounded and had rounded release button.
When the Powermate Jr first came out, they were not included with the canisters, but were listed separately in the catalog at $50. I believe later they started bundling with canisters, and some even came in matching colors such as blue or red (but most I saw were the gray).
I found that the Powermate Jrs on the Kenmore tended to bog down easily when they touched the surface (upholstery etc). I haven't tried the new Pet Powermate that my Progressive has yet.