The PP90M1 is definitely no longer a fringe gun or "That Weird Looking" one anymore. An increase in appears in free for all and death match have made quiet a name for this gun. While a lack of power over other guns do give it a disadvantage in larger fire fights its extremely high mobility and relatively high rate of fire make it a great choice.
A nice combo I was using for FFA was the attachment with the Acog and rapid fire, The gun has an amazing ADS time with the Acog and was a beast for mid-range engagements. unfortunately long range was a bit hit and miss, The Acog does not want to be steady with rapid fire going at range so its necessary to burst the gun, lowering its fire rate. Up close the Acog is a little bit at a disadvantage but more often then not this gun still chews thru people.
All and all I would encourage you to try it, and put a few levels into it, you will be glad you did.
