It works really well - I doubt you'd want to bend the arms too much though as the paint would crack, so pick your pose first and then apply the paint. Here is how it came out:
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For the mud texture I used a product called "no more gaps" which is sold in hardware stores over here in Australia. it sticks like nothing else, and once it's dry you can't get it off. Even scraping with a knife it doesn't want to budge easily. It certainly won't come off with general handling.
The acrylic paint also adheres really well. I think you would have trouble trying to achieve a smooth consistent tone if you were trying to paint a skin tone for example, as there's no primer underneath so the paint doesn't lay down as evenly as it would on a primed surface. In that situation it would likely fail but certainly for the mud effect it was fine painting straight onto the rubber - it doesn't matter if the paint is streaky or uneven because it adds to the effect.
I sold it many months ago and I've had no reports form the current owner that anything has deteriorated over time, so I would definitely give it a shot!