thing is, whoever grabs the potion then just waits to use it at the best encounter too. it ends up being about who has the potion of iron skin during the encounter with the most damage.
This doesn't happen when we play. The fact that it can be stolen very easily forces me to use the potions at the earliest convenience. There are just so many ways that the potion may not end up in my posession at the last or biggest encounter. Also, there are also too many ways to force an all player loss that having the potion at the end is far from a guaranteed win.