They also offer a £10 voucher every time you book, making it quite attractive together with the cashbacks.
Problem with BA's BRG is that BA's price is almost always higher than third parties, so the value of the voucher is not really doubled - and AFAIK if the voucher is used you cannot make a BRG claim on the booking.
Like others said, expect hassle when your flights don't go right. However from my own experience that is the case with most travel agent bookings.