I think generally it would be better if the upgrades would be directly selectable from the main slot window… like for example the way I made it in this quick mockup below:
Clicking on the Red X would bring up a popup to ask you if you want to buy that upgrade and how much it would cost you.
Also clicking on a green checkmark would ask you if you want to sell the Upgrade again in case you don’t want that upgrade anymore for some reason.
Currently you have to tear down the entire slot if you don’t want an upgrade anymore… then rebuild the slot and then repurchase all the ones you actually want… which is annoying at times.
And if an upgrade is not yet available (not yet researched) the check box becomes greyed out or something.
Or maybe make it a scrollable list… don’t know… something like so:
Anything would be better than having to go within the choose window within a slot window.