I have tried I2P, here is my take.

It is amazing, but it has the issue of not having that many user. I2P is great, but because not many people know about it and that it is harder to set-up than going to a torrent site and downloading, not many people use. I2P speed improve the more people use it. One other flow I found is that I2PSnark is awful and there is a need for a better client for it. From my understanding the more you seed, the better speeds you will get, thus it encourages seeding which solves the issue with normal torrent were a lot of people will not seed after a while. I think it is a great idea specially now that many torrent sites are being taken down.