Theh smartvu has chromecast built in, so you are paying $40 extra, and you don't need to use another device to use it for many of the features. It also has ondemand built in, so it will be better in terms of features.
Thanks! Yeah it certainly looks that way on paper so that's definitely the way I'm leaning - was interested in first hand experiences before pulling the trigger :) Particularly how it compares to a plain chromecast (any performance differences, etc? Is it basically identical hardware for the chromecast bit? ) and also how plex performs on it (if it's good I might look at one for myself too)