The rage blade right now is very clunky. It takes 8 auto attacks to fill, but most fight are over in that time. Then once you get it full you commonly just lose it because it times out so quickly. But when you do get it full(most of the time this comes from you stacking it before the fight, not in the fight(also a very clunky mechanic)) it's absurdly powerful, too powerful. For 2500 gold you get around 6000 gold worth of stats when it is full(depending on how you value the on hit damage). But when it's at no stacks it gives about 2000 gold worth of stats, and those are split between AP and AD.
Consider smoothing out the power curve. Increase it's base stats and or reduce the max number of stacks and reduce the max potential. It would also be a really nice quality of life improvement if the stacks lasted 6 seconds instead of 5. Right now the item is not fun to use but it's extremely powerful. It's power in lane is oppressively good because you can stack it on minions and since it's 2500g you can get it sooner than other mid's power spikes.