Having dealt with First Active in the past, my money would be on them decreasing the rate sooner rather than later... There's a reason that there's no end date on the rate: to make you think that it may be in place for longer than e.g. the year that others are promising. From personal experience, I would not expect their rates to last as long or longer than others on offer. That's not to say that you shouldn't put money in there, but stay completely on top of the rate and any rate changes. Do not assume that it will still be there after the other banks' rates expire.
Sprite