They're fund of funds, so the structure results in triple taxation on everything inside except the US stocks(so the US only one is reasonably good, but I wouldn't go for the world one)
Of course in an iDeco it would be double taxation(once in the originating country and once in the US, except for the us stocks held in the vanguard fund).
For the world stock, the management fee is also reasonable but marginally more expensive than creating your own mix. It's not much more expensive though, and it would automatically rebalance the component stocks(japan, developing and developed), which is neat, so it's not a bad deal if you don't mind the extra taxation on dividends. You're ultimately paying some extra taxes and management fees for convenience
If your japanese is ok,
http://siegeljiro.com/rakuten-vt-bunseki does a reasonable rundown on it. Hoping that ideco will eventually offer emaxis slim...
