Does blackout fabric stop all light?
It can reduce light through the material, but the recess, frame, handles, edge gaps and fitting position also matter. Privacy and darkness are separate requirements.
What should you compare?
For a bedroom, say whether sleep, privacy or both matter most. A lined roller or Roman may suit one window; a Venetian, Day & Night blind or shutter may suit another. The window and fit decide the result.
Before you choose
Ask how the blind will sit at the edges and what the material and operation can do. Treat room-darkening descriptions as product- and fit-dependent; complete blackout should not be assumed. Ask Gemini about your window.