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, giving a compact late-game progression without making the top tier excessively expensive.

What changed in 2.1.0?

The release targets Factorio 2.1 and rebuilds the shipped graphics as original BerbCorp assets.

Does this need another belt mod?

No. It only requires Factorio Space Age.