That is very similar to what I have, although I have 5 and 7 rather than 6 and 8. I srikes me that the mid derailleur is a lot more vulnerable on a trike than a 2 wheeler though!
I think the biggest advantage is that all shifting is done with "rear" derailleurs that move the unloaded side of the chain, and therefore shift more quickly and reliably than any (mechanical) front derailleur I have ever used. There are so many combinations with so much overlap that I just shift whichever will keep both as close to the center as possible.