It's a pretty decent trade off. There are ways around the lack of armor training and the Equal opportunity adds to the TWF fun more often then doublestrike. Really the Improved and Perfect balance are the great thing. There's nothing like an ability that justifies dual wielding Keen katanas.
Plus remember with double strike you can two weapon rend even on rounds where you don't get a full attack.
Yes it is if you're a TWFer and high leveled enough to reap it's benefits.
Is it better than a vanilla 2Her? No, but not much is for fighters. On a full-attack it can be though worthwhile though. I recommend you read the TWFer guide.
I keep looking at this and wondering if it's better to just go straight Fighter.
The real draw for the archetype is the level 9 ability, Doublestrike. It's a standard action to attack once with each weapon.
Sounds nice, but as a standard action you'll probably only use this while you're moving during the round. Plus, since you're by definition not full attacking while you use this ability, you don't get the benefit of Defensive Flurry (AC bonuses) or Twin Blades (your substitute for Weapon Training, basically - bonuses to attack & damage). Seems like it's not especially worth it, but maybe I'm wrong?
For a two-weapon fighter I always recommend weapon master and the use of two similar light weapons so all your feats universally apply. Weapon dice damage pale in comparison to static bonuses, especially with a high crit weapon like kukri's.
I prefer brawler myself. It gives you its version of weapon training at an earlier level and gives more static damage per hit (+3 to damage at level 3). That basically covers any lack of damage from using a high dex build necessary for TWF prereqs. It also lets you debuff your opponents' attack bonus when you are next to them, which is always nice. It helps to make up for the lack of armor training to some extent. You can also eventually prevent opponents from taking a 5 foot step out of your threatened area through a combo of two of its abilities.
Your choice in weapons are a bit limited though. Unarmed strikes, particularly from a monk dip, are always popular since they basically has double slice built in. Shield also works since they can serve as AC. My personal favorite though is the cestus, since it has similar stats to a dagger, and you can still hold things in your hand.
The Two-weapon warrior is more accurate though, since the penalties eventually get waived, so they can more easily use feats that sacrifice aim for more static damage such as power attack. The ability to hit twice on a standard attack has already been mentioned too.