If you're looking for something that will be meat animals purely for your own consumption, it's a great mix :). Flemish Giants are just as lean as any other rabbit, but you can get a heck of a lot more meat off of each individual rabbit due to their size.
NZWs are generally the rabbit of choice for meat rabbits because they are lean and muscular, but also because of the color of their fur. When I was raising them for both meat and show, the meat buyer (who had to come down from Canada) said that the primary reason they liked NZWs over any other breed is because stray hairs can't be seen on the meat during inspections. Not sure how true that is, but the market for anything for commercial sale sounds like it'll be a lot better if the rabbits are all white ;).
The only concern I'd have is, how much bigger is the buck than the does? NZW does can get pretty large so the cross may not be an issue, but if the buck is significantly larger than the does there could be issues with birthing, and may be an increased risk of injury during breeding.