I've been using Xfinity TV for a couple of years know via Digital Economy bundled with my Internet Blast! package. When I use the original converter box (DCT700 aka device type JD4082 ) I connect the RCA out cords to a third party DVR (Magnavox) line in and everything works per my requirements (i.e. I can record/watch all of the channels allowed by the Digital Economy package).
I decided to try the same technique in a different room so I went and requested a second converter box (Device type CMD31T) that had RCA out cords (my third party DVR doesn't have an HDMI input). Everything appeard to work OK except I then found out that most of the channels that are normally over the air (antenna available) channels (i.e. 2-25) won't record by my third party DVR while other cable chanels like 49, 72, 273 are recordable.
I hate to think that Comcast is intentionally restricting use of non-Comcast leased DVRs (like phone support tried to get me to believe in sales rep speak) and that instead the cable box has to be changed/re-configured).
What surprised me is that the I could record normally non over the air channels via the cable box but the same cable box wouldn't let me record those channels that were normally available over the air via an antenna.
If only Comcast leased DVRs are allowed then it confirms my understanding as to why people are cutting the cord and I sure won't recommend to anybody using Comcast for normally free TV content. I hated even having to use a converter box when they made it mandatory a couple of years ago but I decided to go ahead if it was bundled with the Blast! package. If nothing else I sure would I had gotten 2 of the original converter boxes I had in the beginning, instead of just 1).