We have a freeview Humax which works very well but does not have HD. there may be HD available in the future when the changover has finished but it will need a different set. We also have a Virgin HD box which has BBC HD and Channel 4 HD. Frankly, not much added value, however the Virgin box does seem to be upscaled on some BBC/ITV channels and can give a very good picture, possibly slightly better than the Humax freeview box.
If you are not going to change your TV for HD, there probably isn't much point in going for the additional cost of the Humax freesat HD box. Also, there can be issues with the siting of the Dish which may be difficult to aim. I put in a freesat Humax and dish for the inlaws as they are so far into the wilds, they cannot get freesat. The setup works very well and is quite similar in use to ours. There are even more channels of rubbish to watch as well!
It is worth keeping an eye on the Humax site as they often sell graded units with guarantees quite cheaply.