I've owned and setup Tivo's for others for over 15 years and everyone I bought was used! That is inspite of the fact I have little good to say about the company and less with the company that bought them out a few years ago with all of their patents (which is why there are no other true "DVR's" made anymore.)
One unit, no adapters, interfaces, additional HDD etc needed or extra hassles to deal with! A 'true DVR'
There are Roamio's available on e-Bay as long as you look for the '846' series with Lifetime service w/ the plastic enclosure and the separate power supply. There are two other models that are CATV only (840 & 848) that have a metal enclosure like all the former models had and internal PS. Stay away from the Bolt, they run extremely hot and suffer from over heating. They also use the smaller 2.5" HDD which isn't really suited for continuous operation like a full size HDD's (3.5"). The current 'Edge' model, the D6F, I don't know much about, but I believe those use the smaller HDD also.
If you are looking for something less expensive, the previous 'Premier', 746 & 748 series I've seen for under $150 w/ Lifetime Service.