This CNET review confirms that in the "All about the remote" section of the review:
http://www.cnet.com/products/roku-3/I can hardly believe Roku would remove the instant replay feature. If they have, that's too bad. Or maybe it still works as instant replay while in-app, but search when in the main Roku UI?
There are quite a lot of remotes out there without instant replay though (I have one). They just have the * button at the bottom by itself, like this:
It sounds like the safe bet is to not rely on instant replay being there.