I was talking about the USB3-ports expresscard.If you buy it without HDD or "erase in save mode" (= erase and rewrite it in random-mode completely 3-10 times) the old HDD/SSD (but that will take some hours depending on capacity) you will be safe. the most safe is to buy without drive and put in your old one or a new one.
in general, you are much more in danger if you SELL your equipment with your old HDD, because if you don´t erase definitely in REAL safe mode it is very easy to recover all your data.