Divided exhaust housings can aid in spooling larger turbos. It concetrates exhaust energy, but it needs to be plumbed right with a custom divided manifold, with the right firing order of the cylinders. I don't think this is a twin scroll thing.
Bare with me as I try to explain this right.
Imagine, using the above photo, our engine, and a divided tubular manifold where only cylinders 1&4 feed the left side, and cylinders 2&3 feed the right. If the firing order and times the exhaust valves open are right, you have constant, and less turbulent, exhaust flow through the turbine housing. In our stock manifolds, exhaust gasses mix and colide with each other, then try to squeeze through the turbo. Divided housings keep it separated and flowing. One side is blowing while the other is not.
I hope this helps and makes sence. From an old edition of S.C.C. I believe they said divided set ups like this are more beificial to 6 cylinders and not to 4's.
P.S.
That turbo, if it bolts to our manifolds, should not be used. The gasses would have to mix, then divide. Major restriction.