Personally, I don't like how those are handled currently, and got some ideas for improvement. Mentioned those a few months ago at IRC, but was too lazy for proper explanation
Anyway, now it is written, so here goes:
First, what we should do when designing the UI and underlying game logic, is to consider how easy it would be for player to understand and to interact with. Which requires understanding of what and when player would want to do with UI controls, and how often. And that brings us to the topic: reaction fire and TU reservation controls.
Why anyone would reserve TUs for firing? To avoid accidentally spending them on moving, of course! There simply could be no other reason. But current design does more: it prevents TUs reserved for shooting ... from being used for shooting! What is the logic behind this? I fail to see it.
To continue with, not only TU reservation, but RF TU reservation prevents player from shooting. For me, it is illogical too: first, any reasonable player would fire a gun only if he got an alien he is able to shoot at, and in that case saving TUs for RF is a bad strategy, since the earlier you have killed that alien, the better; second, firing a gun in UFO:AI requires three step sequence: click the "crosshairs" icon, select firemode, select target; there is almost no chance to do that by accident, so no protection is needed. RF TU reservation should not block a player from firing a gun. He expressed his decision to spend those TUs by following a sequence of UI manipulations and there is no reason to add more -- that will just add extra frustration.
Even more, current system got a rather complex logic with two TU reservation pools: one for RF and other not for RF, which stack, rather than overlap. To me, that seems to be overcompicated logic: if player reserves TUs for shooting ... he just reserves TUs for shooting, not for "one way of shooting" and the "other way of shooting after the first shooting is done, if any". Try to imagine the combat situation when that could be needed!
Most likely, the only difference is whether he will use them for shooting on his turn, or leave them reserved for RF on the alien turn. Hence, two reservation systems are not needed: one is enough.
So, my proposals are:
1) Instead of what we got now, just make a pair of on/off switches, with first of them enabling TU reservation, and other enabling the reaction fire. That should be enough of controls.
2) There should be a global control for people like me who want RF to be always on (could completely remove "RF" button from the battlescape UI).
3) Reserved TUs should NOT be protected from being spent for firing or reloading.
4) A little extra: no "RF firemode selection". RF should automatically use a firemode which will deliver the max damage for available TUs. When alien jumps you from behind the corner, it's not a time for conserving the ammo. You just pull the trigger and don't release it until one of you is dead, that's all.
Opinions, anyone?