Check if HRK is recognized and authorized in your region.
WHY
Since I've purchased more than half of my collection from there, I haven't encountered any problems.
It's generally considered unethical most of the time. I only pay $1 every two weeks for humble.
I have a few sold keys available on Kinguin, it really helps me.
I'm not familiar with HRK, but the value seems reasonable for TW:SW.