I was a Level 34 Commando in Normal mode. I went into Scarlett and tried for an hour or so and it was way too easy. Enemies seemed to be scaled from about Level 28 - 30. That's not strange at all as it's the same max in the maingame in normal mode, appart from a few bosses at Level 31 -32.
What I did was starting over again in True Vault Hunter Mode. To my positive surprise I found out you could actually fast travel to Oasis right after starting the new game in TVHM. In Claptraps place there is a fast travel station, and the only place you could fast travel to was the Oasis, this early in the game. I went in there to check it out. And true enough, enemies was scaled to my Level and it was a real challenge.
So this DLC seems best for people either who are Level 20 in normal mode (at the tops. Smart to have room for Scarlett to level with you up to Level 30) or for those who have finished the maingame start over again in TVHM and access DLC that way.
Another thing I found out when starting in TVHM was that all my fine equipment from normal mode was crap now. So I just sold it. Even cheap TVHM weapons (white) was better than my maxed normal game equipment.