I can't complain about the signing, it's cheap, short, and fills a massive hole in the rotation.
I still don't see Lynn, Cobb, Arrietta or anyone else better than Cashner being signed at this point, and I don't see him being worse than Ubaldo, Miley, Hellickson or Tillman last season so he should be an upgrade to what he's replacing.
If he pitches well and the team is playing poorly by the deadline he can always be traded for some sort of return.