Went to look at that Barclay's club site... Ow, my eyes. Can tell its got some Russian influence thats for sure.

Anyway.. The interest difference isn't as great as it first appears. 9.5% is promised. Within the FAQ you see that its 9.5% every business day. BTC-arbs works 7 days a week. So the interest is still greater on the Barclays site, but its not 10:1. Averaged out its more in the range of 5:1.