I didn't get a reply to my previous query on anyone doing acca refunds, but if anyone else is considering them, I did 2 the weekend on the internationals and both hit the refund - so I should be able to recover about 75-80% of that for profit.
The only downside I see to doing them is they are potentially expensive from a laying point of view if you're doing the £50 ones. You might need to be putting in 150-200quid into each one in total, to try and get a £50 refund, getting all that back and making a £5-10 loss if it doesn't hit. But if you wanted to put 10x acca's on one weekend, and none hit, it could be pricey.