fervent fulcrum
You can go with any sens while aim training as you are mainly focusing on building your hand's ability to control your mouse while aim training. When you play your main game you can continue to use whatever your main sensitivity is. Though the others in this server may not, I recommend that you try to keep your main game sensitivity (while in-game) as consistent as possible so that you can learn it thoroughly and avoid issues with muscle memory not being overwritten for certain distance calculations and their mouse movement translation equivalents. It is possible to learn multiple sensitivities at the same time, but you will be a user of all and master of none unless you really put time into switching between the same sensitivities consistently.
"Why do you feel like your sensitivity is too fast when you go back and forth?" Answer: When aim training, even if you use the same sensitivity as when you play in-game, you may end up changing your form (how you use the mouse) temporarily to achieve the goal at hand. Say you play tactical shooters typically and you are now playing a task in which you must track things over longer distances. You might shift your hand to be less stationary and more "floaty" in order to keep up with the speed. This is no phenomenon and nothing to worry about either, the goal of aim training is to get you out of your comfort zone and train different parts of your hand, so you'll want to either shift the focus of the form of your hand to remaining in that stationary form while attempting the scenario, or you will want to learn to shift forms in order to do different tasks both while aim training and while in-game. If you get better at that form, though, make sure you are upping the challenge and not skipping out on yourself as, though it may be easier to be "floaty" you might also not be as sharp or accurate, which is why you aim train, to make sure that form is both sharp and accurate as it is quick and not just "floaty".
umbral fulcrum