Does this replace turbo belts?

No. Turbo transport belts remain available as vanilla Space Age belts for blueprint compatibility. BerbCorp Belts has its own Mark 4 that builds from express belts.

What are the default speeds?

Mark 4 is 60 items/s, Mark 5 is 75 items/s, Mark 6 is 90 items/s, Mark 7 is 105 items/s, and Mark 8 is 120 items/s.

Can I change the speeds?

Yes. Each BerbCorp belt tier has a startup speed setting in items per second.

Can I change costs?

The iron gear cost can be scaled with a startup setting. The default is 0.5, which halves the More Belts-style gear progression.

Why did the visuals change in 0.2.6?

The Mark 4-8 belts were toned closer to vanilla/Space Age belts. The belt bodies now stay mostly grey, while each tier uses a muted arrow/detail accent.

Does this need another belt mod?

No. It only requires Factorio Space Age.