I've done appeals for my husband both for ESA and PIP and won both. It's very, very worth trying. It's quite usual to be turned down, then to be refused at the mandatory reconsideration stage then the appeal which drags on for a long time has a much higher percentage of winning...
Please always remember that I am always right. I have a framed certificate to prove it.
When in doubt, stop and think... WWSS? (What Would Suzi Say?)
For more info please see THIS thread