Lots of internet wisdom above.
They are the same gun, with a couple of MIM parts being the difference in functional parts. I have not heard of any further issues with rough chambers or MIM failures in years, and the issues were never as big as it was blown up to be by the Remington and/or Cerberus haters anyway. Remington took care of anything they were contacted about and some owners did anything needed themselves, and a few chose to bleat about all Remington quality having gone to hell all over the internet. The "matte" finish on the Express was very rough, and there were tons of complaints about surface rust and all kinds of advice about keeping them slathered with oil. The problem is/was the standard post bluing rinse didn't get all the bluing salts out of the rough finish of the surface, and oil is NOT a solvent for bluing salts. The cure is a warm soapy water bath of all the metal, a good rinse, and then dry well and oil. The revised matte finish they are using now is MUCH smoother, and more real matte matte than sandpaperlike.
The Express has a lower level of polishing, and cheaper synthetic or wooden stocks than the Wingmaster's polished walnut so they can sell it for a cheaper price. You can buy whatever you like, and in our supremely cost conscious environment most people are buying Expresses. The difference is not quality, it's grade.