It's hard to say if this is a good trade for you.
On one hand I have built 25+ "essex" guns as a value build alternative to more expensive brand names; on the other hand, I have built may of them for 300-400 and none of them are able to become truly high tolerance weapons capable of outstanding accuracy.
It's a mil spec frame, and the slide, I would imagine is a mil spec slide. The maker doesn't matter in my honest opinion, as the makers were often just casting/forging companies looking for additional streams of income, and rarely a name that could provide enhanced engineering or brand name appeal. For instance, the maker isn't an HK or a COLT, etc.
If it were my blackhawk I would pass. As for soft metal on the Essex, the slide will almost always be harder than the Essex frame, so you can have your own brand of concerns there over time. It's not worth it if you are looking for a bragging piece, but it may be worth it if you are done with your Ruger, and don't mind just having a shooter, but test fire it first to see if you really want it.
You can check out some more stuff about 1911's and variants on Net Gunsmith || Everything about Firearms
If you have specific questions, I can probably answer your specifics.