It seems weird to me that you get such little benefit from the mini sentry and mini flamer sentry, so here’s some ideas I had to make the 15 vendor point upgrade worth while
first off, both mini sentries should be able to be picked up by hand to quickly reposition them, maybe even letting you unanchor them by hand, this will let them actually be incredibly mobile and let you save them reliably during assaults, or slap them down in the middle of a slug fest/rout. As a side note, you should be able to place them on the same tile as a barricade so that you dont have to unanchor them, move them into the same exact volume of space as before, where suddenly there is plenty of room, then re anchor, it’s tedious and although I get making regular sentries take a bit of work to set up, minis should be easily slappable on the same tile as a cade.
For the mini sentry gun, I think giving it the properties of an SMG (low range, high firerate) would be great, so that it has a fixed range and won’t waste ammo at a random runner at the edge of the screen. I’m thinking its range should be from point blank to about one third to one half the length of the screen, with appreciable damage fall off but respectable damage close up. This will make the mini sentry a great flex defense tool, without being oppressive at long range to make it impossible to deal with for xenos. Setting this up at a chokepoint like a maintenance hallway or a cave will make it require at least a defender to get through most of the time.
For the sentry flamer, since all flamethrowers aside from plasma are shorter range, I’d like to give it a utility aspect. Change the fuel to green, and give it a wide nozzle, so that it can cover a small to medium sized room with green flames, which will slow attackers and clear weeds. I think additionally there should be a togglable mode to fire at visible eggs/weed nodes/vines/etc that are vulnerable to flame, to make it a great terrain clearing tool, but being higher risk to reward by being so close to the danger zone.
I’m not as familiar with the tesla, but if it has a maximum target per second/tick capacity, adding a mini tesla with a weaker effect but hitting more targets would be nice.