I'm going to recommend purchasing the slightly slower and more expensive ram as there is some guarantee of it working. The faster ram may not work, it's not worth the risk IMO.
Here's a decent vid for replacing parts in your machine http://www.youtube.com/watch?v=vEcIer28aNc
Hope it helps
I did a little bit of CTRL+F through the reviews. Some people mention the cheaper one working with Acer Aspire One D270. Though there are a few models of D270, I think they are all practically the same, or at least all compatible with the same RAM. I hope.