The Dinan warranty does not cover the extended period of the CPO warranty. BMW may deny a warranty claim if a modification (including the Dinan tune) is deemed to have caused the problem. Another point to consider with regard to the Dinan tuned X3 28i.
http://www.1addicts.com/forums/showthread.php?t=478612
http://f10.m5post.com/forums/showthread.php?t=1183615
http://www.dinancars.com/warranty/