I am VERY VERY VERY offended by that. Our vet is not only been our vet for 8 years, but is a very close family friend, and that was not fair for you to say that about him. And he doesn't do the injections. We do.
Sorry if I offended you, but I am speaking from a horse owner that has dealt with her fair share of "iffy" vets. Not saying yours is, really, but I do turn a skeptical eye on some vets.
Personally, I would rather try an oral suppliment first, and if the horse responds positively, then great, I can avoid the injections for another while. Saying that they absolutely will NOT work whatsoever is, in my personal opinion, closed-minded becuase I have many many happy customers that attribute their horses' well-being, happiness and soundness to certain suppliments.