Hello Jude.
I come across quite a few people who use these machines. I've had mine for several years now. My case is apparently quite mild, but I was given a machine, because I was getting up in the morning with a mild headache which could develop into a major migraine. I think it did stop that happening and certainly I always use the CPAP.
I'm not sure that it can improve diabetes or hypertension - I don't feel it has in my case, but then it was never suggested that it would. It may be that if I lost weight then all these conditions (including the sleep apnea) would improve independently of each other and the machine.
I hope that helps but it's only my personal perspective on it and we're all different. I certainly hope it helps you to feel better. Getting more peaceful sleep should help and maybe give you more energy to pursue wight loss.
All the best,
Jane.