You decaffinate food/drink with benzene which is cancerous. They probably remove enough or all of it afterwards, but you can never be sure.
I would rather drink freash green tea as it does not contain a lot of caffein(anything at all?), it does however have som tein(correct term?) which has some of the same effects as caffein.
Anyway the total health benefit is great, because little or no caffein and all the other stuff in the tea is very healthy (anti oxidants).
Just eat and drink healthy to optimize your sexual health, looking for super erection results from green tea is like believing in penis pills.