I used to use Mortar Strikes a lot back before I ever prestiged for the first time. Then, I befriended the Vulture, learned about when they did to other people's screens, and stopped using them.
Great to get aliens off you. Being horded by a pack of unruly scouts? Even the basic MS should thin the herd. As you upgrade, they get much more powerful, and if there is a cluster of aliens/cryptids in your vicinity, you can sure bring them down or critically weaken them.
Until you upgrade them once or twice (even thrice), they're really only effective on Scouts or other minor or weakened enemies.
When you unleash them, it's best to close your eyes, and tell your mates to do the same. Everybody's screen shakes like there's a 8.5 earthquake, and the bigger the strike, the longer the madness. In addition, it leaves the user disoriented (the whole team is screwed up, but especially the user).
IMO, the cons outweigh the pros.
ya, we had some fun with this the other day (bc of the cons you mentioned) an we all were doing MS very often to just see what what would happen. It was chaos man! its fun to break up the monotony every once in awhile, but it's super annoying. My side nearly split in two from laughing though. It's like someone is shaking your TV whilst trying to watch The Hangover.
I've never used them... But I've been in lobbies with someone else using them. They've caused me to go down more than once. You literally cant see anything. i kept getting hit, but I couldn't see where it was coming from. Turned and ran... Right into a swarm . I use the vulture and while the rockets on it cause some vision problems, the mortar strikes are 10X worse.