if you like the classic way this is the best one I can recommend:
This is the long version I describe.
A shorter version is available as well, but the sound is not so good as with the long ones.
Affordable price, acceptable quality, low noise, but good deep sound when idling.
In the end at factory noise level.
It is possible to get both versions legalised to a Twin in Germany, so in the UK it is rated as a silent silencer, for sure 😉