Needed to add some more ram to my laptop, had a good look around for a quality brand/price and these seem excellent value, ADATA is a top quality brand, I put 2x 4GB in my X220 to get it to 8GB.
THIS DOES WORK on a PC ignore the for MAC bit on the listing, it will work on BOTH, the seller has 2 listings at the same price with identical part numbers, I did put the PC one on here, but the Mac one is showing.
Also lot of new laptops only come with 1 SODIMM installed so run single channel mode.
These are PC and Mac compatible, seller is very quick to ship. Mine turned up the next day.