Since I cannot gamble to socket it and LAz is my only option is there any reason to not just toss my 0os ETH thresher? Or is there something of value to having 5os given from Laz?

i mean you can make a eth obedience... but i wouldn't really say thats of much value...

There is Doom, but i'm not sure if that's a very popular runeword for mercs. Keep it in stash until you see it needed or try to sell it. There is also Obedience but that too is not so popular, choosing away insight with the meditation aura is a big tradeoff for most people.

I'd be more inclined to use obedience with my Trapsin more than most others. I don't find mana is such a major issue with her. I might consider this.