Ford, Steeda, H&R are others to look at.
When choosing springs, the make is important, but also height, rate and type (linear/progressives).
1. Drop: 1.5 is the most you "should" lower your
stang. More is only good for looks.
2. Rate: How stiff you need them to be? 1/4 racer, street, RR, Auto X? mixed?
3. Type: Linears are "predictable", the best for handling. Progressives give you a bit of "comfort" on bad roads, they are softer on compression start.
I find linears to be the better choice for Mustangs. I had Eibach Pros before i got my MRP springs and its a night and day difference.