Can you use Synchomax in a MT 325i as well?
Yes. I'm running it in my 325i, and way better shifting than factory. I don't know how it compares to Redline. Exact same process for changing. Mine took about 1.7 qt.
I've swapped out the Synchromax. The great shifting it provided only lasted a few months, then was about the same as the factory fluid w/60K miles on it.
I put in Redline D4 ATF for use in the Phoenix extremely hot climate. According to Redline tech support, D6 ATF is closest viscosity to the factory fluid and is recommended, espec. in colder climates (D6 is about 10% thinner than D4, so not much difference -- Synchromax is a heavier viscosity than even the D4.)