I'd like to suggest giving this feat a longer duration. It is really the most effective combat feat the shadow dancer can have, but it's duration is left to desire.
A trade off could be setting the progression of the resistance to 10/4 by level 15, and 10/5 by level 20, which gives considerably less resistance. Concealment, and ac are good as they are.
Right now the duration is one round a level, I would suggest maybe upping it to 1 turn a level.