I read a few years ago on here one guy did a test of effectiveness against carbon and safety vs nylon or some other plastic which is used as a pickup screen in some gas tanks. Some additives are extremely bad for the plastic, turning it into goo, or making it brittle and crumble, but the conclusion was that Seafoam and Techron Concentrate were very effective and very safe, with Seafoam being less expensive. I use both with good results.
As for having stumbling at 10k miles on a new engine, that is NOT indicative of a defect, you can carbon up an engine in 3k miles or less, and its no coincidence that is the recommended interval for most additives. If a treatment improves the stumbling, you can bet it was carbon causing it. Until I learned this, I always used to wonder why a tune-up wouldn't restore smooth idling on my high mileage used cars...
The FP60 and Neutra 131 mentioned above have an extremely good reputation for years on this board, the only reason I haven't tried them is I'd have to order them, vs. buying off the shelf locally.