While for some users, having your giffgaff call balance pop-up after each text or call is really handy, for others it can be a real pain - especially on some handsets where the pop-up is quite intrusive.
Unfortunately this cannot currently be set on or off individually - it is either on for everyone (as it is now) or off for everyone. Personally I don't mind too much either way, though I can appreciate that it is probably more of an issue for those who don't like it than those who do, so I wouldn't really miss it if it was turned off (especially as you can request an on-demand balance by sending *100# anyway).
If you would prefer it to be off for everyone then please Kudos this idea, if you would prefer to have them left on then please add a comment. Ideally I suppose we could have the option to turn off and on individually - but that would be a longer term goal as the system would need to be changed to incorporate that.