I haven't even heard of Odds On - maybe one of the other UK GT'ers has some knowledge of that. You could feed that for a while and see how they do on it, or you could gradually phase in the food you wish to feed. I've never bothered about continuing to feed the food they were on in kennels, because in all but one case I didn't know what they were being fed, so I just switched them cold turkey to their new food. With any new dog, there's usually a period of trial and error until you find a food which they like, and which suits them and also your pocket!
I must admit that Burns is my current favourite (although I reserve the right to change my mind as I have many times in the past ) but it is quite low calorie compared to some foods so you may have to feed more than it says on the bag to keep their weight up. Actually I like this about it, because it means I can give them nice big meals which satisfy them and I don't have dogs that are hungry all the time. I also like the Burns Penlan Farm pouches, which are partially organic, and mine share one for breakfast and/or mixed with the kibble.