They made a range of shotguns of varying quality. There were, I think, 4 different grades of sidelock, and numerous boxlocks, and they were still advertising hammer guns before the war. Jeffery didn't actually have their own workshops, but farmed out the guns to the trade. Generally well regarded.
The company is noted more for it's rifle developments. They were responsible for introducing a number of cartridges, of varying success; the .600, the largest commercially available shoulder fired sporting cartridge until the advent of the .700 H&H; the .450 & .475 No. 2, the .500 Jeffery, the .400 3" and it's cousin, the .404 ( probably the most widely used dangerous game cartridge before the introduction of the .458 WM), the .333, and several lesser known rounds.