I didn't order from DMC but the company I ordered from literally put the exact item description and commodity code for the SN and it still passed through customs no issues. SN isn't an explosives pre cursor nor is it illegal to posses at least in the UK so it would likely only be seized on the basis of the item didn't match what the sender had put it down as.
As for welfare checks, I have never heard of anyone receiving one, the system here is stretched to capacity, I don't believe they could perform them even if they wanted to so I wouldn't worry.