We too use Harry hamster and have never had diarrhoea ever. I think it is a good food. However I don't know about the P@H mix. The regular mix has been noted to contain too much sugar which is not good especially for dwarfies. Sometimes foods contain 'hidden' sugars in ingredients such as molasses so I would check the side of the pack
If you do decide to change over you should make sure you do it slowly by gradually adding the new food to the diet until you have swapped. This allows the gut flora to adjust to the new food.