kinda like importing your own car. it's a grey market thing. legality nobody has a clue really. people who say it's legal or illegal actually have no clue other than what other people had written.

if you want COA sticker, buy windows 7 coa sticker. last i bought was RM65. windows 10 can use win 7 serial.

if you want cheap keys, get those volume keys in peeshop or lazatda. volume keys got expiry date, so in command line, type slmgr /xpr to check. some do sell retail keys, or other keys. there are types of licenses that are not meant for you, like LTSB, N (not for malaysia), etc.

anyway if you don't mind the watermark popping up from time to time, can just use without activation/key. nothing will happen, can use pc like normal.