Happy camper with 283's, 285's (GN110 ft)the same power but 285 has variable power settings and a variable coverage lens on the head. Used with an "L" bracket or grip gives no strain on the acc.shoe of the camera. All accessories are interchangeable between the two except the high power module for the 285. Several aftermarket bounce cards and diffusers were made for these flashes.
They're excellent units to start with.
A Guide Number is always going to be an approximation, a starting point for your system. If GN110 is used and your exposures are a little off don't worry, use your own #
FWIW a GN is arrived at by testing the flash at a distance of 10'/3.5m and determining the correct exposure using a flash meter or film.
So, f11 @ 10' =GN110 with ISO 100 film.
Using the calculator dial on the flash you can determine different GN's for different film.