There is no tracer variant for this type of magazine.
In version 2.0.6, there was a bug where you could not refill PDW magazines. It was later fixed in version 2.0.7.
As with all magazines, combining two of them together will get you the sum of both magazines filled into one, while still retaining the other. (Assuming there would be rounds left over in the second magazine.)
It's the one of the longest ammo capacity magazine in the game