Can you use it on plastic without ill effects?
Yes. You immerse the model overnight (or longer if you like) in a little pot of disinfectant and it softens and lifts all the paint away - varnish and glue too. Then gently brush the paint away with an old toothbrush. Plastics are fine although I wouldn't like to leave them in for a week (although someone else on another forum did say they had done so without ill effect), and I wouldn't use it on a soft plastic like cheap toy soldiers are sometimes made from.
Wear rubber gloves! That stuff isn't nice on your fingers and can make your skin sore if you're doing more than one model.
Don't rinse in water until all the paint has come off. Dip the brush in the disinfectant to scrub at stubborn bits. Once you rinse in water, any remaining paint will re-set. If there's a lot of paint still in place, just leave it for another night.
You can even drain the disinfectant to get the gloops of paint off and re-use it (for paint stripping).