So, I can't provide much evidence about personal impact, because oral health is long-term and also diet dependent. I can attest to the lower psychological cost of flossing with water than flossing with nylon or silk.

Most of the studies on the subject are produced by the people that make the product, like this 2009 review by their PR manager, and so there's a serious risk of systematic error in the reports (I'm under the impression that this is the case for most dental research). That said, the reports claim it is more effective than flossing manually at reducing gingivitis and bleeding. Removing plaque is mostly the toothbrush's job; while flossing is generally intended to remove interdental plaque, it's not clear silk or nylon does a good job, and it's not clear that those reductions actually result in less caries.

If your primary reason to floss is to remove interdental plaque, then my first-principles guess is that the alternating compression and decompression of a high-frequency jet is better than just rubbing silk or nylon along it, by analogy to powered toothbrushes outperforming manual toothbrushes, but I would not consider that position conclusive.