At first blush, Holy Locket was ripe for heroes that could make use of its cost-efficient stats and healing amplification. Dazzle and Necrophos were prime candidates, with the latter also benefitting from his own scaling regeneration skills. With their passives were reworked from magic resistance to health regeneration, heroes like Pudge and Huskar could make use of the item, even if they lacked healing skills. Finally, there was Timbersaw, whose Reactive Armor’s regeneration was buffed in 7.20, where Holy Locket seemed like an ideal fit with its stats, magic resistance, and regeneration.
In practice, however, the item has proven lackluster in several aspects. In its use as a support item—amplifying healing for your team—consider its price point, 2650 gold, and the alternative items you could buy, such as Force Staff, Eul’s Scepter, Rod of Atos, or Glimmer Cape. Even on Dazzle, one of the meta’s top heroes, the item has been omitted among professional teams in both support and core roles. Matumbaman on Team Liquid will often transition from Guardian Greaves into Solar Crest or Hex, and Forev on J.Storm tends to move into Force Staff. These all provide utility that’s arguably better for your team than the regeneration from Holy Locket. The saving grace for Locket then might be its efficiency as a big stick of stats.
But being a good value item might not be good enough in this meta. Holy Locket exists in an awkward space as a transitional early to mid-game item, which is currently occupied by stacking multiple Wraith Bands, Bracers, or Null Talismans. Timbersaw, for example, could transition from Bracers into Eul’s or build towards a Lotus Orb or Bloodstone. These items help mitigate either his mana issues or his weaknesses against silences. The same item timing awkwardness runs the same for Huskar, who transitions from Bracers into core items of Armlet, BKB, Halberd, or Pike.
As with most new heroes and items in Dota, they don't always stick their landing. Holy Locket is a good item on paper, but not yet in practice, which means it could be a few tweaks away from being overpowered.
Kaya, since its introduction, has been an underwhelming, with Storm Spirit being the only hero who built it as a core item. Patch 7.20 introduced Yasha and Kaya and Kaya and Sange and opened up a few interesting new builds.
With movespeed now being percentage based, the recourse for slow heroes to catchup on speed is the Yasha component, which adds a constant +25 on its own and +35 when built into its next tier item. Or you can just build it on Skywrath Mage and speedboat around the map.
The other valuable stat for heroes building into Y&K is its attack speed bonus. Storm Spirit, who lost his attack speed from Power Treads, sorely needs to makeup for it. And then there’s [hero-outworld-devourer], whose Arcane Orb scales with his mana pool and attack speed.Na’Vi takes down PSG.LGD at Megafon
Y&K has given reason for Intelligence heroes to consider Kaya, more than it has for Agility heroes building Yasha, when Manta Style or S&Y is out there. There are some hybrid Agility, magic damage dealers, such as Shadow Fiend and Venomancer that can make use of Y&K. But the Kaya component here isn’t as useful as Yasha is for Int heroes. They don’t need the manaloss reduction, and if Venomancer wanted to deal more magic damage, there are more impactful alternatives in Aghanim’s Scepter and Veil of Discord.
As for Kaya and Sange, it has been more niche than its counterpart, built at nearly half the rate as Y&K. If you built Kaya, and you don’t want a Yasha, then you’ll probably will build this item. Zeus, Skywrath Mage, or even Ancient Apparition might build into it, even for its slight boost to the Kaya component. Where the item can be interesting is on tanky heroes like Timbersaw, Ogre Magi, and Bristleback, depending on how much you value Status Resistance. But like with Holy Locket, K&S here might not provide enough utility at a 4k price point to be part of their item builds.