The 50 is much thinner than the 70.
Very basic look at it:
the 50 gives you a smaller profile and faster sink rate.
the 70 gives you a slightly larger profile and slower sink rate
You can play around with different weight bucktails and pork.
Montauk regulars prefer bucktails with extra hair for buoyancy and the #70 rind.
If I have time tonight I will take a picture of both sizes side by side.
FYI - the containers will leak if you don't keep them upright and the pork will dry out if you don't keep it in the liquid.