As I've stated in the Suggestion thread: I'm one of the very few dps mercs who play GROUP RANKED. That's queueing for ranked with 4 people (so many people fail to understand I don't mean solo ranked). A merc does insane damage in group ranked - if left alone. On my server, smart teams caught on and realized that the best way to counter a merc dps is to sit on him. Because the current meta is PT tank / 2 hatred sins / healer, I had a PT Tank and a Sin tunneling me for most of the game. What do they do? Interrupt me, of course.
If done right you can negate every second Barrage proc of a merc. Because Barrage has an ICD of 8secs and Priming Shot will most likely be ~17s cd with Alacrity, every second Barrage proc needs to be triggered with a TM hard cast. Interrupt that and not only will the merc be unable to cast TM for 4 secs, he also wont get Barrage. ****s up our rotation.
Sweeping Blasters does the same thing for Mag Shots. So it's not a new mechanic for mercs.
This is a huge mobility buff if you know how to use it. Reading the forums however, I've gathered that most people don't get it.