The unexpanded shell has no distortion to the face. If you place it beside a regular coin, you will see no difference. The advantage to this is, it looks just like a regular coin, absolutely no distortion. It's very crisp looking. The disadvantage is you have to get the matching coins remilled to fit the shell which is expensive if money is an issue. The remilled coins are slighly smaller to fit the unexpanded shell, but no need to worry about the spectators noticing. You can't use this shell with any other regular coins, it must always be used with the remilled coins.
The expanded shell does have a slight distortion to the face. If you would place this beside a regular coin, for awhile, it probably would be noticed, because of its slight distortion and size. It is slightly bigger than a regular coin. This would be the disadvantage, however, you most likely won't place the expanded shell and the regular coin right beside each anyway, at least not for long, so it probably won't be noticed. But the advantage is you only need one expanded shell and can use any other regular coins with this shell. It's more versatile.
So both shells have a plus and minus. You just have to see which works for you.