From what I can see they charge 0.5% per transaction and offer a 'near interbank' exchange rate. I actually don't think you would make any profit on this one.

On the transactions where you earn £8 from transferring £750 or more they would charge a 0.5% commission (£3.75) on this transfer and then you deduct the small skim from the near interbank rate you have probably have no profit or you could actually have lost money.

Can you only redeem the points on your 4th and 5th transfers? if so you are only really recouping your losses from all the fees and profit would be slim to none. Personally giving this one a skip, but happy to hear if any of the above is wrong.