I would recommend a separate inverter simply because the are so much less money and if either the charger or inverter section should ever fail, you're not out both units.
If I didn't have a converter already, I might consider a combo but they are very expensive and heavy. We move a lot of Xantrex Freedom 458s to the field and to dealers for large motorhomes but haven't seen very many in Airstreams. I like the Xantrex Prowatt SW a lot but like mentioned, there is no reason to stay with Xantrex, they just make pretty good stuff.
Converters, Inverters, Monitors, EMS, Zamp Solar