Despite the negativity about cards by some, I have been looking into this topic myself. As Magic Static notes, it depends a lot on what software you plan to use with the card, and that will in a large part depend on how comfortable you are with Linux. There are guys like UpdateLee who can make these cards do darn near anything but that is because they know how to compile their own software - by the way, if you are into that, search on his name because he's written some software that works with those cards, that he makes freely available. It's far above my comprehension level, but maybe you are more on his level than I.
Then there are people like me who just want to watch TV and don't care to dig around in Linux, nor understand the nuances of compiling software. My understanding, and please be aware that I am speaking here without benefit of actual experience, is that if you use MythTV (or Mythbuntu) it has a certain amount of baked-in support for these cards. There is a list of supported cards, including some TBS models, in the DVB-S section of
this page. There are
setup instructions here, although those seem to have been written some time back.
Having said that, if you ask in these forums people tend to make it sound like it's very difficult to use these cards to their fullest potential if you don't recompile MythTV, or whatever PVR software you're using, with some kind of additional code, which is something most people won't do. And the fact is that most of the people in these forums just buy set top boxes, which often have built-in PVR support, and many will have no idea what you are talking about when you start talking about PVR software like MythTV or TVHeadEnd. I have looked all over to try and find a post by one actual, real person that's using one of these cards with MythTV under Linux to record and watch programs, and I have yet to come across anyone doing that. And I think that's a bit sad because if folks would really get into that mode of operation they'd find it offers a lot of benefits that you would not have using a set-top box.
The biggest benefit, in my opinion, is the potential for using multiple tuners so you can watch one satellite signal while recording another, or record two or more different satellite signals simultaneously. Another benefit is that when you use MythTV as your backend software, then you can watch live or recorded programs on any computer or device capable of running either the MythTV frontend software or XBMC (using the cMyth plugin). And, if some new format comes out and they release a new card to receive it, you only have to replace the card, not an entire set top box - not that I think that's real likely to happen in the immediate future, but you never know. And a final benefit is that if lightning hits near your dish and knocks out a tuner, you might only need to replace that tuner card and not an entire receiver.
Everybody has their own reasons for doing what they do but if you are really wanting to try a card, and especially if you have any inclinations toward getting into Linux, I would say go for it, and don't be too discouraged by the negativity. But if you do, just understand that not very many will have taken that path, so when you run into snags it might (or might not) be more difficult to get help.