The only real downside to buying it is the fact that I only have 23 coins. If xur sells something I really want next week like the jellyhorn, hawkmoon, thunderlord, or read death ill be kicking myself. Ill be able to get 9 coins from the weekly. But, Im not a no-lifer. And probably won't have enough time to grind the rest out.
Then don't buy it. You have Icebreaker, which I assume you keep equipped most of the time. Either it or Mida would get neglected in use.
I bought it last time it was sold. I'm a scout rifle user and I don't have an exotic special that I always use. So for me, it was a good purchase. Still, if I want to use my Gjally, I have to switch to my NITC.
Mida has one glaring downside. [b]Lack of range.[/b] My NITC and Badger both out shoot it for distance. Outside of that, it's a terrific gun.