The only thing I know about them is that they are promoted to death by Spencer Matthews and various members of the Made In Chelsea cast.
That alone suggests to me that you should steer well clear of them.
If they were any good, I suspect they'd have a better quality ambassador -both in terms of more A list persons who were willing to endorse them and in terms of what they could afford to pay someone to promote them.
Most weight loss diets/products attain a certain level of credence because female celebrities who are under massive pressure to - basically - be under weight thin either disclose in interview their diet/products/methods or gossip columns reveal it. I've never heard of anyone legit or A list endorsing forza raspberry - so highly doubtful.