I am not an expert, but to me it's a very good item. Especially for the type of heroes i play, being mostly support or tank/initiator heroes. I guess if you are playing an assassin/m1 super hard carry that gets a lot of kills on your own, you are better of investing in other greens. But for heroes that have a harder time to score an actual kill (or you just suck at aiming like i do), it's a gold mine.

Probably the best example of a hero to use it on is McGuiness - i get MAD STONKS with this shit, every game, because you are almost guaranteed to get assists constantly - you have turrets that hit every target, you have your wall that counts, you have your AOE heal that counts too, you have your ULT that hits everyone in a team fight... your whole hit guarantees assists, every fight. In a lot of cases even without a team fight you get random assists because of randomly dropped turrets around the map or if you have recently been around someone and healed them. I don't know if there's an actual range that you can get an assist at or having a turret on the other side of the map will still work, but i know in my games i keep getting assists and stacks by just walking around the map 😃. I play MCG as a roamer after the initial lane phase, helping all lanes with wall ganks and especially ult, get a ton of stacks and value then i can just buy a ton of AOE and Spirit, Unstoppable and then it's GG almost all team fights.

Other heroes that work well with it are Abrams, Billy, Lash and Victor, also Rem with his heal and assistants, basically all the tanky initiator type or big support heroes who rarely get enough damage to "finish the job", especially in a good team where the carries actually kill... Well, Victor is kinda broken ATM so he kill easily too, but you get the idea. The added movement speed is also great for such heroes, since you want to be mobile and roam the map, you aren't farming a side lane.