I read some of those posts initially and was concerned once I needed a CableCARD, but I never had any trouble. I didn’t need one until I got an HD Series3 TiVo and Verizon FiOS (I actually didn’t know what they were, I thought you only needed them for premium channels). The dispatchers ***did ***seem to have trouble communicating that I needed a CableCARD to the installers, cause it took three tries before they showed up with the right equipment (first they came with a cablebox/DVR, then one S-card, then finally they happened to just have an M-card in their van that wasn’t even intended for me!) Can’t say if this was deliberate or not (maybe hoping I’m an idiot and would just ditch my TiVo and take their DVR instead!) But once I got one it worked flawlessly. They also did bill me for both the S and the M card for like a year (even though the tech took the S when he gave me the M and assured me they wouldn’t) but they eventually refunded me the difference.
When I moved and switched to Optimum cable it took their tech like three hours but he finally got two S cards working. He swore M cards wouldn’t work, which concerned me because the TiVo forum says to always use an M instead of two S’s if possible. Two S cards cost more per month than one M so maybe it was a scam. He did keep having to reboot my TiVo every time he changed a setting, and that Series3 took like 7 minutes to start up! What’s odd is that a few months later I kept missing recordings and would get blank channels. Figured I’d try an M card instead of two S cards and this time I just went to their office and got one myself! That turned out to be the problem, two S cards seemed to put more of a load on the TiVo box than an M (I would have thought otherwise). Installing the M card myself was simple, just called and gave them the host ID and it worked.
Same thing when I switched it to my new Roamio. And I happily found out that M means ‘multiple’ streams as my Roamio Plus can decode six channels at once (I though I’d need three M cards, one for every two tuned channels).