Got to agree with you on this one.
I waver between the £10 & £8 goody bags usually and I've always got loads of MB of data left at the expiry date.
However, this month I thought I'd try the £6 goody bag and you guessed it, I'm nearly out of data and I've got another 3 weeks to go.
The moral of the story for me, is to buy the bigger goody bags, as you never know when your going to need the data, as that's what's happened to me this time. 🙄