I assume that is a picture of it, looks really clean. I purschaed a 2015 Rubi HR about two years ago with less then 15K on it and love it!
I don’t think there are any specific issued related to the Rubi HR to be aware of. There have been reports of head issues with 2013/14 but those seemed to have been worked out by the time 2015 models came out. I suggest taking a look underneath for any damages, leaks, etc. Make sure to take it for a drive and engage the 4WD on some dirt road or parking lot. I suggest engaging the lockers to see if they work. Also try the anti-sway bar disconnect, they have been known to have issues as the electronics upfront can get wet and then corroded, but that wouldn’t necessarily stop me from buying it.
Is an auto or 6sp? If it is an auto it will either have 3.73 or 4.10 gears, if 6sp it will have the 4.10, unless someone special ordered it with some special setup. Of course this assume it is stock, which it looks like It.