The KMC X8 has, I think, nickel plated outer links.
Doesn't matter except for looks. The plating of outer links is not what wears in chains.
Other than that, it claims to have mushroomed rivets
Every chain today has "mushroomed" rivets. These rivets prevent joining the chain again with its own rivets, a clear drawback. However, they make shifting possible under load. You don't need to shift under load on bikes powered by human power only, but for e-bikes the mid-drive doesn't turn off the torque quickly enough when you stop pedaling, so shifting under load is something that is unavoidable. So you want "mushroomed" rivets on e-bikes. On non-e-bikes, you probably won't want "mushroomed" rivets so you can re-join the chain again using its own rivets, but oops, "mushroomed" rivets are only type of rivets you can find.
Fortunately, Shimano has solved the rivet issue with reinforced rivets that are single use only. They allow you to break and re-connect the chain over 100 times (assuming the chain is over 100 links long). It costs some amount of money to buy enough of these reinforced rivets for your emergency toolkit, but they weigh next to nothing.
With other makes than Shimano, you can only use "quick" links, a misnomer since they should be called "slow" links instead. The reason is that although a joining link of this type is quick to be installed, and quick to be removed from a chain that is clean, if you go out and actually ride your bike the chain becomes dirty and the dirt makes joining link removal so difficult that it's almost impossible without special pliers.
Because Shimano allows you to use reinforced rivets, whereas other makes demand you to use these "slow" links, I recommend Shimano chains. A mini chain tool is smaller and lighter weight than joining link pliers. Besides, a chain tool is something you in every case need because you need to shorten the chain to its proper length prior to installation, so you can't omit owning a chain tool. But you can omit owning joining link pliers.
and the X-Bridge outer plate.
Nothing in the outer plate affects the property of interest, how fast the chain wears. Only the half-bushings that are integral to the inner plates, and the chain rivet, affect chain durability. So you are definitely interested in the quality of steel used in inner plates and rivets, but the quality of steel used in outer plates doesn't matter.
Does that make it a better quality or more durable chain?
No, not any more durable.
Focus on the quality of steel on rivets and inner plates. The steel should be chrome hardened. That makes the chain much more wear resistant.