And very loud.
I would not use one for trail riding unless you are literally miles from anybody, and certainly not at any kind of designated riding park made for public trail riding.
A closed course (motocross track) is where these are used.
There is a YouTube video of a WR250R rider (with a foreign accent) who adapted a muffler from some model/year YZ, and while he did install it, it looked, to me, as if it stuck out like a sore thumb since it was obviously just a Jimmy-rig to make it fit.
But, he seemed to like it.
What lots of WR250R riders use is the FMF Q4 muffler (and Powerbomb or Megabomb FMF header pipes if you want).
These ARE made to fit your bike, give a power boost, weigh less, sound good, and are not so loud that they'll wake the dead.