I also got bit by this. Razer's simpler wired keyboards and mice might be OK, but their systems are fundamentally broken.
The Razer Blade Stealth (7500u) has broken Thunderbolt 3 / USB-C support. Most popular devices simply won't work at all, even though they work with other Kaby Lake computers, and even though they work with Razer's own previous Stealth laptop (6500u model).
The Razer Core has broken display software (double vsync lag) which makes it not work properly if you use an external GPU and monitor (which is ostensibly the purpose of the device)
Additionally, the Razer Core's USB ports just flat out don't work. There's a power short of some sort in the internal USB hub, so that if you plug in a device that draws any more than the lowest amount of power, it cycles through a connecting/disconnecting state, looping forever.
All of these are fundamental flaws with the product itself, so you can (and will be asked to) RMA units over and over for eternity, but you'll never get the problem fixed.
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Razer Support has known about all of these issues for months now. There is zero communication coming from Razer -- they won't discuss their design flaws, they won't support their devices, they won't even acknowledge these issues as happening.
When asked directly, the CEO claimed he "wasn't looking at product reliability because we're actually one of the top few in terms of product quality". - https://www.reddit.com/r/razer/comments/5v8zkh/improving_raz... Since Razer's leadership doesn't care about quality at all, I can't imagine the company will ever care either.
At this point, I'm not spending another dime with Razer ever again, and certainly couldn't recommend any one else do so.