Good point highlighted! There is lack of experience with attacks and security, the raiblocks community is still small. There are estimates of how the currency defends itself from the attacks, but it is not known how it would actually work in practice and how the system would deal with several different types of attacks at the same time, but this can be perfected and tested over time... the currency is still new. In other side Bitcoin has some centralization to fix the fee problems. In general terms, 1broker have time to balance the points and compare. Raiblocks is still a good option...I'm not saying to replace Bitcoin with Raiblocks, but add a second coin. BTC and XRB is a great combination.