Then what is the advantage (if any) of this Split Y vs. some 5-plug daisy chain cables made by some other companies?
The advantage is the ground lift. All daisy chain cables I have seen share a common ground at each point. We eliminate the number one cause of noise, a ground loop, by lifting ground.
As I stated before, isolated power for each device is the only sure fire method to eliminate all noise problems caused by interaction between pedals. This is the main point of the Pedal Power line of power supplies... Isolated Outputs.
We simply offer a method to gang up pedals on a single output for situations where there is no other easy solution. While we do make an effort to make this as noise free as possible, by lifting the ground to one side, it is still less than ideal to gang pedals up on a single output. You have to test what pedals you will use together in order to find pairings that will play nicely together.