OPINIONS ON EXHAUST SOUND

To be honest, that does look like a Flowmaster, and Flowmaster numbering system is very similar, 5 numbers (or more, for newer delta flow)
But fm's number for that would be 42541 (40 series, 2 1/2 pipe, first 3 digits)
Your says 42451, I suspect a Chinese clone of an FM.
NOT saying a real FM would be quieter or sound better.