I would say you are comparing two different levels of suspension. The 4100 AST set would probably be more apples-to-apples and frankly, you couldn't go wrong with either set.
Two benefits that Feal suspension will have is a company that is highly responsive to communication from the customers and easier access to rebuilds.
The quality is also there with AST, but all your communication/rebuilds will essentially be going through a dealer rather than direct.
I believe rebuild costs are comparable. If you can find a lightly used set of either one at a killer price, that would be an easy way to decide.