the main problem ive found with the npcs leading you to hunting is the actual quest is completed when they 'show you where the beasts' are. they will run almost into the mouths of the beasts and then say 'here they are'. so if you kill all the beasts first with the npc then he won't run to the spot and you will miss out on completing the quest and reputation bonus. i think the strength of the npcs can be a problem sometime but usually it is relative to the armor they are wearing. diego unfortunately has only light armor so he only works well if you can let him use his bow light other hunters. one of the best npc's to take with you in myrtana, he's available early on too, is cyrus in cape dun. he helped me with the trolls, monsters, and gargoyles east of the temple of trelis. after each battle he was down to a couple of hp's but he stayed alive. but really if the npc's were good at fighting it would encourage you too keep them around for too long and therefore make you a worse fighter. even if your not a mage you have a healother scroll in a quicksave spot when you have a npc accompanying you. also i've noticed, especially in nordmar, that npc's will engage beasts which are near them but also through a wall or hill. when you hear someone grunting in pain from attacks i would save the game and then, even if reloads are required, find this npc and save them. because npc's only move when they are in a certain radius from you. take for example when one npc joins you and you make him wait and then another joins you. the first npc will head back to where you found them, but they will only be walking when you are a certain radius from them. this means you should be careful where you leave your npc's as you may think they are fine but if you are near where you left them with a new npc in tow they will be walking alone and will soon end up in some beasts belly. i had huge problems with this when following and loosing the guy who leads you to the different clans.