Pure fighters and barbarians do not have a good self-healing ability unless they have an extremely high healing amplification. It takes around 40 cure serious to heal back up to full health. My suggestion is to remove the -10 to all stats debuff on the silver flame potions.
They're Bound to Character and requires 400 Silver Flame Favor so it shouldn't be overpowered. By the time they have enough favor every other class would have an equal if not better self-healing ability. Maybe replace the stat damage with a longer cool-down timer or a different type of debuff to increase their use. Fighters and barbarians could use some better self-healing potions or stronger potions.