The software on the THR22 is basically the same as the software that was on the HR10, which was basically the same as the Series 2 DirecTIVos. A few standard TiVo features are crippled, most notably multi-room viewing. Current generation Series 5 TiVos (the Roamio line) have a number of new features (like built-in Netflix and Hulu apps) that are not available from DirecTV.
Re an eBay box, if the box is truly new, then you should be able to activate it. You could ask the seller for the RID and confirm with DirecTV that you can activate it.
Current Setup: 2 Roamio Pros, 5 Minis on FiOS (all with lifetime)
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