I'd be most scared fighting these if I'm alone or just a couple of us and its like a large pack of them. I've seen a documentary on hyenas and they're nothing like dogs, they're worst and they're pretty strong too.
Their basic bite attack is their weak spot. If you have an ac of 15 or more their attacks will most likely miss. They have a lot of hit points though for a lvl 1-2 party. Past a level 3-4 party they should be easy enough.
If I were a GM attacking with Hyenas I would focus on using trip, once I down a PC I would try and surround it with Hyenas. Thus pinning it and causing the PC to be prone.
You are a dirty GM! Like you said I don't think they would do much damage if you're like well armored or in a group, but if your alone in the forest or wherever then you're at risk. Even with armor they will still try to get you to fall... They've like done it with elephants!
Heynas are pretty fast too so if you're on the run from them they'll catch up. I was just reading this: