Graphene oxide (GO) can improve cementitious materials, but its effectiveness often differs among commercial products even at the same nominal dosage. This study proposes an optical microscopy-based framework for evaluating the initial dispersion quality of commercial GO suspensions before cement mixing. Under fixed slide preparation, imaging, and image-processing conditions, optical microscopy was used as a geometric dispersion-evaluation tool rather than a direct chemical characterization method. Three image-derived features, namely projected boundary richness, coarse-agglomerate fraction, and spatial dispersion uniformity, were integrated into an optical initial dispersion quality index, $D_j$. The framework was applied to five commercial GO products at a fixed dosage of 0.03 wt% of binder. The $D_j$-based ranking was Brand 1 > Brand 2 > Brand 3 > Brand 4 > Brand 5, and remained unchanged when the coarse-agglomerate threshold varied from 20 to 100 μm². Bootstrap resampling confirmed the robustness of the ranking. The 3-day compressive strength increased from 51.1 MPa for the control mixture to 52.6~60.8 MPa for GO-modified mortars, corresponding to enhancement ratios of 3.1~19.2%. The strength-enhancement ranking was identical to the optical dispersion ranking, with a Spearman rank correlation coefficient of ${\rho }_s=1.0$. The proposed $D_j$ index provides a practical pre-mixing screening tool for comparing commercial GO products before strength testing or detailed physicochemical characterization.