Dates with a unique design always seem to be quite popular with collectors as it is usually much easier to collect coins by type rather than date - especially with coins from the Royal Mint such as bullion Britannias as we never know if / when they will be released! The 1997 gold bullion Britannias were not released until 2003, and then only as part of the Royal Mint Type Set.
If you like the design on the 2007 gold Britannia or the date means something to you, we would recommend you consider buying one sooner rather than later as once our original delivery is gone, we can not guarantee that we will still be able to source them.