I'm just going by what I've used. I used some vet stuff lol hugry all the time, imagine that? A girl gave me some stuff out of her office that was a bright read and had alittle sting to it. So, I don't know.
I never said you couldn't mix oil and water in the same syringe, I just have had poor experiences doing it as have some others that I know. Basically, I think the difference in absorption rates between the two (water absorbed faster than the oil) leads to more soreness post-injection. I've never had this issue (soreness the day following injection) mixing water-water, but I have with water-oil. (Jurox Susp & B12 = no prob, Jurox Susp & Sustanon = sore, unless I do 2 separate shots..Duh).
As for the B12 - I use calvet supply stuff and it is fantastic. No pain, no sting. 100ml for $6.99. I love it and use 1ml (1000mcg) three times a week.