MotorFizz Camping Seat bag

[Pylie]

Has anyone tried one of these?

Are they any good as a substitute for panniers (12GSA) which I really don't want to fork out for just for the odd overseas trip...

Can be seen here

http://www.aerostich.com/catalog/US/MotoFizz-Camping-Seat-Bags-Small-Medium--Large-p-16405.html