Its not a matter of turning it on/off at will. You get a finite amount of uses (2 in the video) and then thats it until you meditate. In the PAX video, Geralt is way overleveled for that quest, that Wyvern barely did any damage to Geralt when he hit him and he was nearly dead when Geralt used the thunderbolt potion, so I wouldn't take that as a knock against potions being "OP".But when you have a potion like Swallow, the ability to turn it on and off seems OP as hell. Superior Swallow healed Geralt super fast in the PAX demo. He was pretty much invincible the whole time it was active. Now imagine being able to turn that off when you're not taking damage and then on when you are. That whole minute of invincibility has just been extended longer than it should have. And if Geralt doesn't use the whole dose by the end of the battle, he can just save it for another fight with his inner off button.