IBM has bought Informix because Informix holds a patent on some database tricks that DB2 needed desperately. They can't just kill either of the two because DB2 is their little pet, and Informix is the worlds most used database (yes oracle claims they are the biggest, but oracle is oracle, nuf said)
As for the pro's and con's, those only exist if you are comparing with something.
There are no pro's or con's to informix if you have no alternative.
