On top of the obvious product placement (the main characters are all based off of older Sketchers commercials) and excessive flirting done by children, the show has no educational value, implies that violence is the only way to defeat their enemies, has no visible role models, and uses inappropriate words constantly (stupid and butt are among the most common). The show is flat, boring for anyone with an education higher than second grade, and far too violent for anyone younger than twelve.
The lack of role models and positive messages is what concerns me the most. There is Grams (the grandmother of one of the children) but she encourages her grandson and his friends to go off and fight. There is a complete lack of concern for their welfare, as demonstrated when her grandson breaks down an old water tower which is not only dangerous, but also illegal. She does nothing to correct his behavior and doesn't even attempt to talk them all out of their violent tendencies even though they blatantly put themselves in extreme danger.
A final concern would be the monster they fight. Most of these monsters are engineered, or forced, to destroy and hurt people, but the children simply go off and kill them without even trying to help them, implying that anyone dangerous (bullies, for instance) should be treated violently and given no chance to redeem themselves or change. Young children invariably see violent characters in these types of shows as the bullies of their school. This show encourages them to use violence to break down anyone who tries to hurt them. Anyone under twelve should not watch this. Anyone over twelve might be able to watch it if they're mature enough (i.e. they understand that violence is never the answer and this is entirely fictional and only meant as a form of entertainment).
I don't recommend this show for anyone that needs to be babysat and I put it on my 'do not watch' list, right next to Kick Buttowski.