Mixed Bag Meaning

(idiomatic) something tending to have both good and bad results or characteristics; something having a mixture of advantages and disadvantages.

Example: Any bag containing a mixture of something.
  a mixed bag of nuts
By extension, a group of entities with few characteristics in common; an assortment.
  The people I met at the support group were a mixed bag: some were grouchy pessimists, and others were cheery do-gooders.
  Owning a car is a mixed bag. It is convenient, but also costly.
2011 January 22, Phil McNulty, “Aston Villa 1 - 0 Man City”[1], BBC:
  It was Villa, however, who posted the next moment of danger with another long-range effort from Young, forcing Hart - who had been a mixed bag throughout - to dive low to his right to save as Houllier's side continued to perform in a most encouraging fashion