At tier 5 it gives only medium bonus speed with the full set. That's low at tier 5.
I'm unsure how overpowered it would be at very high, but I can clearly see at medium it's not very impressive.
This, and the Shadowsun Stetson, should get their tier 5 counterparts bumped from low to medium.
I'd type in more depth, but i'm kind of rushed. I think this is good enough for those TL;DR people.
I wuz racing with dude in full Merc. Not impressed. Its a useless bonus IMO. Coz i need movement speed when outrunning rockets and SUCH! But for short distances medium s.i. just useless. And there no looong enemyless tunnels ingame to cry " Кто последний, тот мешок!!! "аnd then mercilessly outrun ur comrades. OOO Must add a 3sec Very high increase when u start moving after standing for a sec. So u dash a little and then ur speed decrease to normal. That will be asom for these who use Callahan and Merc. set ( both shots =1 sec i guess...and then u dash for 3 sec to safe location. That will compensate " Stand still to shoot" rule)