OK. Just to update this thread.
I bought the Sure Signal V3 and it seems to work just fine. It took about an hour to sort itself out with the Vodafone network, but they say it can take 6hrs, so it did OK. Now have a good signal all over the house and calls are crystal clear.
For the record, I'm using a Netgear DGN2200 (N300) ADSL2, my download speed is only 3.5Mbs but I'm only going to ever be using one of two phones on it at any time. The router has UPNP turned on. Didn't have to make any changes to the router at all.