The thing you must remember is that unless the muffler is specific for the Liberty / Legacy (Which I doubt it will be) is that it will produce a difference sound (& drone maybe) to other cars.
Magna Flow are extremely popular in the US, & from what I've seen, their build quality is actually pretty damn good.
A mate of mine had a set of his Tiburon & it actually sounded really nice
To some degree, there's a bit of trial & error with mufflers as some members on here have experienced in order to obtain the right sound, volume etc.
Personally, I think it's worth a shot, otherwise, if you want to be safe, stick with a brand that has been used by members on a regular basis (Hitech for example - Wouldn't be my personal choice btw). That way you can get a good idea of what your in for.