3: Let me compare the item with Luden's Echo.
negative:
- 20 AP
- 10% MS
- active has a 30 second cd, Luden's does not (~5-10 seconds charging, depending on champ)
positive:
- 300 Cost
- 300 HP
- 10% cdr
- active has 100-250% the damage of Luden's passive (basedamage, scaling stays at 250%) + more targets or multihit with reduced dmg
- the 300 range dash that is completed in 1/4 of a second; 71% of flash range
Luden's Echo is already a decent item to rush, if one wants to push it for early kills. Now for comparing those stats.
- 20AP: definitely something big when looking for an early kill
- 10%MS: good for roaming and helps sidestepping, doesn't really contribute to raw combat though. It's basically just an increased chance to dodge a skillshot, which already exists
- cooldown: Only a few champions can trigger Luden's twice per 1v1 skirmish, so the cooldown is pretty much negligable. Thus, I will now compare one use of Luden's to one use of HRB
- 300 gold: Definitely noticable. That's either enough money for boots (to compensate 10% ms), or to get cloth armor (another combat stat; zed still exists, and other champs use basic attcks too)
- 300 HP: Makes an enormous difference in combat
- 10% cdr: not exactly noteworthy for burst-poke, but a slightly extended fight can already make it worth. Like how champions might fight that would consider this item. Fizz comes to mind, without spending too much thought.
- +15% ap scaling (assuming the player only hits 1 of the 9? projectiles)
Now comparing the combat that involves activating HRB once, and Luden's once. A typical AP caster combo converts about 300% AP (I'm being generous here)
Luden's; player has a minimum of 100AP:
- combo damage : 300 (only counting ap scaling; duh)
- item damage: 100+30
HRB; player has a minimum of 80AP:
- combo damage : 240 (only counting ap scaling; duh)
- item damage:
100 145+75
That's on level one. The base damage on a realistic level - say, 6 - would be + ~45
So the direct comparison at this point is 300+ (100+30) = 430 against 240+ (145+75) = 460. And with every tiny extra piece of Ap, this difference grows. We didn't account for the extra hits for 15% yet
Assuming that the both opposing players built, Luden's on one side, and HRB+Boots on the other, the player with HRB now has an advantage in CDR, HP and damage, while taking a minor hit in MS. Obviously this scenario is highly convoluted. A slightly more realistic scenario would be, that both players first rush a manafixer, that for the sake of comparability will be the exact same item on both sides. But that also means that the HRB user profits more, due to additional AP that is converted by the AP scaling. I'm well aware that it's technically a skillshot, but please think about this: Who likes a combination of AP, tank-stats and mobility?. I'm thinking about: Fizz, Diana, Udyr, Ekko, Akali, Katarina. Basically everyone loves mobility, but there are a few noteworthy examples, like Ekko, Udyr and Fizz. Those that already manage to come up close to land an easy hit, but now get an extra tool to close gaps, become an annoyance to hit with skillshots and even get some more tankiness to survive that easier. meanwhile casters don't even look at the 300 range. The immobile ones can use it to some extent, I admit. But what about the active? Imo this part sucks balls for ranged casters. The projectiles can miss on long ranges, and using the mobility part defensively (when some annoying melee is already in your face), negates the damage entirely, because the blast doesn't fire in the opposite direction.
TLDR:
You're introducing a pretty good item here, that rather profits Assassins than casters, and I don't like it. I think the mechanic is interesting, but will either be broken good and then needs to be nerfed until everybody goes back to buying Luden's. And that's not the point when introducing a new item for more diversity. And please: before you nerf champions that somehow abuse that item to the fullest, consider removing it. Rito's history of jungle items and champion nerfs connected to it gave me serious ca... headaches.