Well, if you've got any other Network titles, you know that their encoding can be hit-or-miss at times. Sometimes it's superb (Strange Report, Robin of Sherwood), other times less so (The Baron, horrible transfers and dirty unrestored prints). I've just gotten today the Umbrella versions in the mail, but haven't looked at any of them yet, though I have read the liner notes. Umbrella houses each disc in a seperate Amaray case, and I believe Network uses double Amarays.
Umbrella's versions include at least five commentaries, loads and loads of image galleries, music-and-effects tracks on two episodes, and introductions (I think to camera) by guests stars to certain episodes. And a vintage 1963 Roger Moore interview, though I haven't seen this either.
Network's version may be cheaper, just,for an American buyer, but for quality of extras I'd go with Umbrella. Conversely, I plan to pick up the Network Colour set for the same reason -- quality of extras