My experience shooting with a friend's DW Pistol Pack (MANY years ago) was good, overall. The only downside I remember was if you shot it fast for several strings of fire, the barrel would get hot (like any other magnum revolver); but the DW has the cylinder release right below the rear of the barrel, on the crane/yoke. When the barrel got hot, so did the cylinder release latch.
Make sure he has the barrel wrench tool; without it, you can't get at the recessed barrel nut to change the barrels. There is also a little feeler gauge for setting the correct barrel/cylinder gap, but if that is missing, it's fairly easy to find a workable substitute; not so much with the barrel wrench.