"Potions are 1.5 times more effective on this unit" might restrict design
This forces all potions to have even numbers for (de)buffs effectively halving the granularity of change you can make to these types of cards. As we have learned from Hearthstone having too low numbers and granularity to work with can make balance changes really hard to make.
E.g. if it turns out that a potion card is too strong giving +10 STR but +8 is too low to be played the choices are to keep it too strong or make it unplayable because if 9 was a sweet spot, it couldn't go there for obvious reasons - what, is it gonna give +13.5 to witchers? I don't think STR is ever gonna go in half-steps.
This forces all potions to have even numbers for (de)buffs effectively halving the granularity of change you can make to these types of cards. As we have learned from Hearthstone having too low numbers and granularity to work with can make balance changes really hard to make.
E.g. if it turns out that a potion card is too strong giving +10 STR but +8 is too low to be played the choices are to keep it too strong or make it unplayable because if 9 was a sweet spot, it couldn't go there for obvious reasons - what, is it gonna give +13.5 to witchers? I don't think STR is ever gonna go in half-steps.