I'd say anywhere around level 20-30 is a perfect time to use it. You get decent weapons, and unless you're really lucky you haven't found any good legendaries that will trump them. End game you most likely will so it makes it pointless to wait.
GT: lIl Nemesis lIl "You can run, but you'll just die tired"
I was soloing with Axton and used a key at lvl 30 and got 2 shields, meh. I was co-oping with 3 friends with Maya and used a key at lvl 25, don't remember what I got on the first pull, but I was able to open the chest unlimited times after that for the rest of the session, it was nuts. Filled my crew's packs top to bottom with purple gear and banked tons of cash selling stuff.
I just killed Angel so I am getting ready to face Jack and the Warrior so maybe I will at least until after that battle to see what I get. After that I will finish up all the side quests, etc. Not sure I am patient enough to wait until 50 (even though weapons might be better).
I am not sure when I will even get leveled to 50 as I might start a new character after this PT. Axton right now and would like to have a few more characters to choose from when doing coop.
Thanks everyone for the input.
I will be on finishing up the game tonight if anyone is interested in joining.
After beating the Warrior the first time, I got some pretty damn good weapon. I had a Legendary sniper rifle drop for me.
I haven't started PT2 yet, I'm still farming other enemies to get weapons and shields to prepare myself, and I've leveled up 3 more times. I did Warrior again last night, and again about 20 minutes ago, and I got even better weapons. This one revolver actually outclasses that Legendary I have.
I absolutely hated Lynchwood, it was such a hassle and I kept getting torn apart. I had trouble at several points in the game, and especially during the run to get to The Warrior. That was awful, I died a lot.
But like most of the Bosses in the game, Jack and The Warrior were pretty manageable, didn't die once.
Now I can kill the Warrior, even with him being a couple levels above me, in just a few minutes.