Mitchell's wool fat  bar soap vs their shaving puck is there any difference between them?
I was able to pick up a hotel sized bar of Mitchell's to try it out and liked it.
Ordered a Puck and dish from amazon since I couldn't find a refill puck by itself.  
Will there be much if any difference between the "sample" bar and the full size puck?

Mitchell’s refill

I’ve used it exclusively for several years now.  Good stuff

Shaving soap has ingredients added that makes for thicker, denser, slicker lather over regular bar/bath soap.
Bar soap lather will be looser, more airy, with less cushion and glide and will break down quicker. One would be more likely to experience shaving irritation if using bar soap instead of a soap specifically designed to shave with because it is not as protective.

On another note, Mitchell's Wool Fat is the latest European shaving soap brand (others include Tabac, Geo. F. Trumper's, Truefitt & Hill, Haslinger, Speick) to move away from a tallow based formula.