Only off the shelf short pipes I have used was a laser system, bought used, not sure of current availability but quality was pretty good and rust didn't kill it even in winter use and neglectfull commuting. However it was a bit of an infernal rackett for early starts. However I never had any mot issues with it or any grief from police, it was rather that it got on my nerves at 6.30 am on the ride to work as I didn't want to be waking the entire neighbourhood, especially in snow where traction was an issue
due to low ground clearence on the sidecar.... as an aside, quite a few of my exhausts over the years have been assembled by cutting off rotted silencers on 4 into 1 systems and welding on alternatives, best was a bsa rocket 3 'raygun' silencer from the 70s that was the best I have ever had for quality of chrome and inproved horsepower, only time I could routinely powerslide the outfit in every corner. Mosf unorthadox was my mate usingba fergy tractor exhaust in that manner, not too loud, decent power and looked surprisingly good after getting a slash cut and can of black spraypaint. Just beware if you have a centrestand as a lot of exhuasts seem to not cater for a stop for the stand to prevent chain contact, easy to remedy but also easy to miss.