Caroline - We attended the show at Tablao Cordobes about 5 years ago. If you have not seen a flamenco show, it is probably worth doing, although I don't think that the dinner option looks too good. It's a cold buffet. However, the guests who are there for the dinner may get first choice at the seats in the theatre showroom, which is not a trivial factor in assessing the evening.
Unlike the flamenco shows we've seen in Madrid, which were in a nightclub setting, with the guests seated at tables, the show at Tablao Cordobes is sort of a theatre style, with the audience sitting in extremely hard (painfully uncomfortable) wooden chairs which are pretty much crammed together tightly. Therefore, if taking the dinner option would give you the choice of a good front row seat, that is something to consider seriously.
Despite the dreadful seating arrangements, the performance itself was quite good.
We made our reservations online directly with the theatre. You would be wise to compare that option to the price offered by BDT.