The Reserve Shooter is a sidegrade for the Soldier and Pyro that basically allows you to switch to it 20% faster and minicrit enemies launched airborne by a bunch of ways except for jumping and airblast in exchange for 2 shots in the clip. 
Compared to the stock shotgun this just doesn't feel great to use since you trade a bunch of consistency for maybe a bit of situational damage that just doesn't feel worth it a lot of the time. It's also competing with some of the best secondaries in the game so it really just doesn't have a whole lot going for it. I'd honestly rather use the stock shotgun over this and for Soldier you definitely lose out on the Gunboats which is just a little too huge of a drawback for me while for Pyro you really just don't even get to enjoy the main benefit of it anymore so there's really not much of a point unless you're some reflect god that launches rockets onto people's feet, launch them, and then minicrit them but then they'd also be flying away a bunch of distance so you also won't even get that much damage in....you get the point. Just use stock or flares or something but if I ever catch you with the Scorch Shot I will be VERY disappointed. 
I don't know, maybe you guys can prove me wrong and to be honest I'm not that fun of a person anyway. But here's a few of them for the people who love the weapon. Other than that, cheers.