Could we have boosts that are based on usage rather than timers?
Maybe even a combination of both? Like timers that only count down while in use?
For example, if you used charges, any ‘on kill’ boosts would deduct a charge.
If you used the hybrid method, then the timer would only go down while in combat.
I typically don’t use any sorts of boosts because I tend to mess around more than anything, I can’t stay focused and really put these things to reliable use, thus I got stacks of them in my bank completely unused :P