I was using M4 full exhaust. It's just another full exhaust which are plenty on the market. Just make sure you modify air/fuel ratio that matches the full exhaust by using a power commander/flashed ECU/or equivalent and off you go.
My 17' R3 came with 1k miles, as well as an M4 Street Slayer slip on. The exhaust was one reason for me choosing a used bike. It also had frame slider, fork sliders, and the integrated taillight when I got it. All I was gonna say is judging on the slip on version which cuts the CAT off the bike, making it similar to a full system without a new header pipe, the bike is very loud. During warm days of riding, its almost too loud. I wear ear plugs and its still alot. I don't mind it but after a few hours of riding it gets to be annoying.
In my opinion, I would save the cash. If you plan on keeping the bike, look into the slip on version as its not too pricey. If your gonna sell the bike within a few years just buy new tires XD
i have the full Ti M4 exhaust and it didn't have the insert when I bought it and the sound was a bit obnoxious. I called M4 and they said that the system was designed to be used with the insert and that I was actually losing power by not having it installed.
Even with the insert, I wouldn't call the system quiet, but it has a nice sound(for a 321cc bike) and looks really good. Also, I can feel the difference in the lower revs with the DB killer installed.