[Darren69]

A twin adsorption silencer will be quieter than a single one. I like the look of the Termis too. Just saying. There are plently of cheap chinese slip ons on ebay (£50) that will fit a monster and they actually look ok, but they are cheap and probably won't last long. Plenty of s/hand Termis too (£250-300) .

I know what I'd fit to mine if it hadn't come with a full system already. Any slip on is unlikely to add any HP or torque, just more noise. A full system if you can get one will add around 10% more torque and hp (well it does for the quattro motor, not sure about the new ones) and it will sound nice too. Plus you will probably get your money back if you sell it on or it will add value to the bike.