Honestly, this series is unironically more interesting than the main one. Sumi's growth and experiences as a rental girlfriend is refreshing compared to the somewhat generic romance of Kanojo, Okarishimasu. Granted, you could say that without the main story existing, we wouldn't have Sumi's pov in the first place. Overall, I'd say this is the equivalent of the Gun Gale spin-off of SAO that focuses on another character.