As Commenters have pointed out, there are lots of things that can kill pretty quickly... but still, awesome weapon right? Could there be a reason, other than plot for the anger? That gun would be cool in theory, but expensive to produce, operate, sell, and then there is the legal costs when they get on the public market. So if I'm trying to make a sale-able product, that's more of a black hole of financial lose... Remember a company's goal is to make money, not create weapons.
The Shrink/expanding suit while more expensive overall and has a smaller market the thing would need to be repaired often, and because that version is almost 100% going to stay in the military arms market you are keeping any legal losses to a minimum while maximizing your economic gains. Further, the overall shrinking/expanding technology has loads of other markets from medical, to shipping, to plumbing... and think about how it can revolutionize space travel and colonization. When you look at it like that, the technology is worth far more than a neat gun.
And a third possibity is that the company is under a government contract. In which case the failure to deliver on the contract would result in lose of contract, meaning money, and future contracts. And most contracts make it so that the government owns the patents on that stuff and having something that doesn't work which produces a beneficial results isn't hard to replicate and as such isn't worth the money to continue finance a company that can't get it to work or to produce such items because they likely already have a company that is much cheaper that can produce those same results.