I finished the teaser, but not as I was supposed to, I don't think.
Unfortunately, I never got the chance to fire a single gun shot. I accidently dropped my gun because the lower area was completely dark so I had to use the flashlight. I think you should be able to use both the gun & flashlight at the same time as a player.
Only major downside was the weird sprint acceleration thing which blocked the strafe functionality. It just felt awkward. I've never seen that in any other first person game. The melee combat felt awesome and the environment too. I'm looking forward to see the final game.