Depends. Some of the Century Arms L1A1s have Imbel receivers, some of them have Hesse receivers, and some of them have Century Arms receivers.
If it has an Imbel, then it's worth the $400.
Don't get the ones marked with Hesse. They're inconsistent, and Hesse can screw up an AK receiver...
Century Arms-make is still up in the air.
Dunno, it can be a bit of a crapshoot with Century Arms. Sometimes, they turn out pretty good rifles. Sometimes, I'd be scared to chamber a round. Make damn sure you inspect it before you buy it. It's not like buying a Bushmaster.