Has anyone used both of these? Is there any advantage of one over the other? Pros, cons?

I would suggest that you get a back mount vest as a feature check. It will make you feel comfortable and you will not feel pain in your back and you can stay in your vest longer than front mount vest. It will make your flying experience as a joy.

FYI I can manage to stay in front mount vest for 15minutes and I stay in back mount vest once for two hours without taking it off. The camera I am using is jvc gy-dv5000 minidv camera which weighs around 6.25kg(13.78 pounds).

Regards
Leigh