Supreloin is a 6 month implant rather than the jab I believe. I know my vet advised against this as it can have negative affects on anxious or nervous dogs. Once it's in it can't be removed without a lot of trouble.
I tried the monthly jab - I think it was called tardac - when I was considering castration for one of my boys. He can be a bit nervous/mouthy with new people/male dogs sometimes so wanted to check the removal of his hormones wouldn't make his nerves worse! The jab seemed to make other entire males less forceful with him and he them but otherwise I didn't see any difference. However with the vets support it gave me more peace of mind about considering castration which we have now done about 4 months ago. He's still the same loving yet neurotic personality as before, after castration, but he has less bother with other males now, is more settled somehow and definately over time more focussed on us when out and about. Still having to practice training though.
I would suggest speaking to your vet and a behaviourist if your question is due to behaviour they really helped us.