I agree with SpeedTech products being the best bang-for-buck kit given the selections available with any of their kits. I can also agree with SpeedTech's top-mount kits carrying on the "older BMW Inline-6" exhaust note because of the unequally-lengthed runners.
SpeedTech's bottom-mount kits are a different story because of the runner design, for both banks going into the T4 flange, being mirrored. Due to that, their bottom-mount kits sound pretty similar to 4n bottom-mount kits, DocRace top-mount kits, and any other popular companies that sell equal-length manifolds along with their single turbo kits which carry a clean exhaust note everyone looks for when switching to a single turbo.
Not to mention the open-dump wastegate note on the SpeedTech bottom-mounts have an aggressive / deeper tone like twin-wastegate single turbo kits out there, since the flange is divided between both banks rather than being merged like the DocRace DR700 bottom-mount kit or On3 top-mount kit, to name a few.
Last, if you look at some pictures of the SpeedTech bottom-mount kit, you can't get more OEM+ than that...you're not required to relocate anything for install aside from removing any parts that have to do with the twin turbo system.