You can definitely navigate with it as an IFR GPS, since it's certified for approach and en route IFR. What you can't do, since it's not a NavComm, is actually tune in the VOR or ILS transmitters, like you can on a 430/530 or GTN; there is no VHF receiver in it, like in the others. For sure you can't do a full ILS approach with it, since it provides no vertical guidance, especially since it's non-WAAS. You could enter the waypoints along the approach and "follow along" with it while also using a true NavComm (which is what I do). For an ILS approach, though, the localizers are not in the database (at least the one near me where I practice), so you need to use the airport as the final point of the approach - which may not (almost certainly isn't) collocated with the localizer, so there will be a difference. For ILSs I use it exclusively for situational awareness and fly the needles on my NavComm.
It's a good GPS and fits my personal mission - but I know its limits and want to make sure Bob S understands what it is and isn't. If the plane he's looking at has a true NavComm as a second radio (e.g. KX155, KX170, etc.), then the plane can do pretty much any GA approach out there at least to LNAV mins.