I didn't know they had a WP plugin, but I used the web app about 6 times this week on a project. It is very fast and easy to use. I do a lot of work on a Chromebook and editing .po files was one of those tasks that I always had to switch over to Ubuntu to do. I fell in love with the web app and how quick it made the process. Just going through the task of editing po files was faster than working in poedit in Ubuntu.