These appear to be STG-58 parts kits built onto Imbel upper receivers. It has the requisite number of US parts to allow it to legally have a pistol grip. That I noticed, the US parts are 1) a shiny aluminum cocking handle, 2) a DSA pistol grip, 3) the magazine follower and 4) the magazine floor plate. I'm guessing that the trigger and/or hammer are also US made. As with most of these, the barrels are high quality (made by Steyr) and have chrome lined bores and chambers so they are generally very shiny and in excellent shape where it counts. Unfortunately, they chose to not include the folding bipod, however you can buy original STG-58 bipods in Shotgun News for $20 so that's not so fatal.
A friend of mine bought one and we had to search through four of them to find one that didn't have noticeable cosmetic problems. These are all built on mostly used parts and the sheet metal handguards usually have a few dents. The "finish" Century puts on them appears to be paint which is easily scratched off. The quality of the paint job varies from crappy to adequate.
When we got it home, I tore it down, sandblasted the old finish off and refinished it with satin black spray-and-bake Norell's Moly Resin. It looks super now.
In the process of disassembling and degreasing it prior to refinishing, I found a lot of crap (hardened cosmoline, etc) in the nooks and crannies, along with spots of rust here and there. Century spent as little time as possible putting these together, so it would be worth your while to do a complete tear down and clean up prior to trying to use one in ernest. That, or send it out to a professional to have it cleaned and refinished (should cost anywhere between $150 and $200 done right. Check
http://www.arizonaresponsesystems.com for one well known FAL gunsmith).
For the $650 my friend paid, I think he got a decent deal. Its hard to find one of these in any condition for less. Add $150 to the price you pay to have it refinished and you'll have a nice example of one of the great battle rifles of the 20th century.