Win10 from HRK

Past that, I've seen OEM keys for cheaper, so it may be. HRK doesn't have a good reputation on their sourcing and G2A-network-based sales, but I don't think they're known for providing dead/revoked keys.
That said, the above wasn't a joke, despite its presentation- extended support for Win7 lasts till 2020; if you don't absolutely need Win10, I'd recommend sticking with Win 7 until then. Win 10 is filled with bugs- some rather significant, like the Windows Update-based one that's currently randomly shooting my processor temp up 45C, has quite a few design issues that occasionally frustrate, and has suffered from deliberate user-sabotage by the designers in its updates. Meanwhile, it doesn't really offer anything more functional than 7, unless you absolutely need the newest version of DirectX. In that case, I'd recommend a dual-boot setup, and just load up Win10 whenever you specifically need it.

Well, your prerogative. I'm pretty sure OEM keys go for 5-8 on the low end, though, with 12-15 being fairly normal, so look around a bit more before deciding to go with HRK. And when you do buy from them, be careful they don't stick you with G2A shield..

It seems unlikely that all but the smallest handful of OEM keys out there are stolen, given that they can easily be acquired legitimately. OEM keys are freely sourced for the purpose of computer manufacture and resale (which is why you can buy them from retailers such as NewEgg). (Put another way, anyone who wants to be can decide to be a "computer manufacturer".)

Retaining a computer with an OEM copy of Windows installed on it, rather than reselling it, is a violation of the terms of service.. but it happens pretty regularly. Past that, I seem to recall that promotional copies are given out somewhat regularly to schools, and I believe sometimes even alongside purchase of hardware components.

Futher reading:
http://www.zdnet.com/article/seven-perfectly-legal-ways-to-get-windows-7-cheap-or-even-free/
http://winsupersite.com/windows-7/no-oem-you-windows-7-oem-packaging-not-individuals

^ this.

For an OEM version to be legit it needs to be on the same invoice as the device.

...proper

Than made me chuckle :)

just fyi, i used old pc, 5years+ .Only upgrade SSD, everything work fine with Win 8.1 its far better than Win 7 in my opinion.
Still thinking to get that Win 10 OEM or not... the price so tempting

As microsoft says -

The best way to migrate from Windows XP to Windows 10 is to buy a new device.

I want to go to the crappy planet where I have a statue and people worship me :P

Raising this thread from the dead a bit here, but ...

No, there are other ways to pay for things on HRKgame. The only way it even takes Bitcoin is via g2apay. If you are using g2apay, then you can pay with Paypal or CC, after some decent sized fee % is added.

"How can it be so cheap?" -- various ways. most utilized? it's free for students, get the 'windows multiple pack', it comes with home, pro, and education version.

"Is it cheaper somewhere else?" -- yes.

I bought the $20.99 Windows 10 Pro Retail (-3% with allkeyshop3 or allcdkey3 or some code I don't remember), so was like $20.35? Then back to around $21 after the payment fees were added.

The OEM version, you can find on "essentially" reputable sites that sell it for $10 or so & I'd use one of those places instead of hrk.

If you check Kinguin, you'll see this Windows 10 Professional is their second best seller, but $32.04 is way too high. If you're going to buy it from Kinguin, there are dozens of other options. Gamivo has some pro OEM for ~$10, from 99% people -- but, even this gamivo price should be cheaper. You'll notice on Kinguin, this exact same $32.04 price is shared by 29 different people. For gamivo, the € 8.00 is shared by around ten people, so, again, they are imposing some minimum there.