What one-to-one actually means
Each natural lash gets exactly one extension bonded along it, isolated from its neighbors so nothing sticks together. Your final density is therefore your own density — classic lashes make what you have longer and darker, they do not add fullness. If your natural lashes are sparse, classic will look elegant but thin, and hybrid is the honest recommendation.
That isolation is also why a full set takes around two hours. Speed at the lash bed is how lashes get glued together, and glued lashes are how natural lashes get pulled out.