Replay TV - My Favorite
Commercial Advance is/was a feature that automatically skipped commercials on recorded or delayed programs. The handy feature was discontinued due to a lawsuit by the MPAA wherein Sonic Blue (the former maker of the RTV boxes) had to cease and desist incorporating the feature. Nevertheless the advance equipped units can be found on eBay for under $200 - depending on the size of the hard drive.
The older units are best since they have the discontinued Commercial Advance feature. The 50XX has a bit better video quality than the 4XXX and earlier models. The 50XX series came in the 5040 with 20hrs of record time and the 5080 with 40hrs. The 5XXX Series has been considered the top ReplayTV unit in terms of features. These units also had the Internet Video Sharing features enabled. Consequently that's why that model line is not being made anymore.
The 55XX line is almost identical to the 50XX and is not as expensive due to the lack of the above mentioned features. Although the newer 50XX series has to have a subscription - you may want to do as I have and get both a 40XX model and a 50XX model to take advantage of the subscription reduction. My 4120 has a lifetime subscription and Sonic Blue has a multi-unit discount of half the 12.99 monthly fee. I added my 5080 to my existing 4120 account and now have 2 RTV units running for half the price of what just one TiVo monthly subscription would cost - and my Replays have MUCH nicer features. Here's a great site for more info on all models Replay TV FAQs. It has loads and loads of information on RTVs including how to upgrade the hard drives to get more hours of record time and other assorted tips, tricks and modifications.
If you are one of the families that have yet to go High Definition -- and are wanting a great DVR ... RTV would be the best Standard Definition DVR for you - in my humble opinion.
Home Theater PVRs/DVRs