For me the Mercury reads the midlane much quicker than the sonic line and is very smooth on the backend. Compared to my Boom you can line up in the same spot but you will get a different look to each ball. The boom goes a few feet longer and snaps harder on the backend. It isn't very close in my eyes to the Ultra Sonic. For me the Ultra Sonic went forever. It depends what you are looking for, I think the mercury will be best played going up the boards when there is a decent amount of head oil and some good backends.
thank you,
Justin Godfrey