[AlexanderHowl]

Maximum Duration is really only appropriate for switchable and beneficial abilities that you would normally use indefinitely (Extra Attack does not really apply). Takes Recharge (-10%) would give a minute of use before requiring two minutes of recharge, so 10 seconds of use and 20 seconds of recharge may be an equivalent limitation, since it would have a 1:2 ratio of use:recharge. A 1:1 ratio of use:recharge would likely then only be worth only -5%.