Adam,
Actually I got mine for £90-£100 on preorder with the MK802 stick (that is still in the box). Not sure what its selling for now but I agree a dual card is a more powerful and versatile option.
My sat feed is remote from my main MythTV/XBMC (Acer Revo 3610 so limited to USB/network tuners). With PVR support in XBMC (along with its various issues that could screw up recordings on MythTv although I think I have ensured that wouldn't happen) it made a few things a bit more attractive (I do have a Tevii S660 and had no-end of trouble with that locking up and needing complete machine reboots)
With that and all the mucking about to combine freeview and freesat channel lists in MythTV and the fact that I dont watch huge amounts of TV, I can keep my existing MythTV system for freeview and if I want to watch the HD channels (and the occassional freesat only channel) I can do so by switching to XBMC and using the MOI/tvheadend/xbmc combo. I have no interest in recording HD as it just takes up more space and I delete recordings once i have watched them
Therefore it kind of works quite well for me but I admit I am probably not the norm.
I will give MuMuDVB a go but suspect I will fall back to what I now have with xbmc/tvh/MOI.
I know some work is being done to try and run the MOI as a MythTV slave backend which I may go down if it works but my aim is simplicity and minimal maintenance once its running and not having to keep rebuilding/patching so we shall see
Martin