Is Alloy more efficient than Tempo to generate graph metrics?

When I check Alloy document, I saw

The same service graph metrics can also be generated by Tempo. This is more efficient and recommended for larger installations. For a deep look into service graphs, visit this section.

I know both Tempo and Alloy can generate graph metrics. However, I am a little confused by this sentence. Is “this” refers to Alloy or Tempo? Which is more efficient? Thank you!