Mongoose with decat is a good choice but a 59 is ear bleedingly loud and imo sounds pants with a decat. No real note to it just loud and er....loud. I have a Mongoose cat back (not the 59) with decat on my ST and it is just right for me. The Mongoose on its own was disappointing. Rumbled a bit more but didn't sound loud tbh and when really pushing it didn't make any sort of special noise. Can't go far wrong with Mongoose for quality, price and sound as long as you get a standard system with a decat. Milltek exhausts are good too but pricey. Scorpion systems are also have a good raw exhaust tone.