I tried to make Beth and Ethna work, I really did, but there are simply better options for me. I can see some use in Beth and I use her ocasionally (against Rakans for example). Note: I only use her in GWO (AO is just 2x Lushen for me). She's basically a single target nuker that needs less setup then your 'average Joe' nuker. She's especially good against units with HP based skills/heals and teams with revivers. I've runed mine fast, because you want to kill before you're killed. She can dish out acceptable damage and her 2nd skill isn't bad either. But I always ask myself "Why do I wan't to use Beth over say... Copper, Buildozer or Kahli for example?" Especially Copper and Buildozer can do high single target damage, ignore defence (so Will runes won't be much of an issue) and they can survive a hit or 2. They also don't need devilmons since summoning skillups is relatively easy.

Don't even get me started on Ehna... 'Theo Slayer' they call her. Well, her buff remove is unreliable and if you can't kill Theomars in the first turn, you've most likely already lost. But since she's not the topic of this post, I'll be quiet about it.