They are the same cells with the same efficiency but provided in different formats. C2523H is packaged with 20 single-use transformation tubes, each containing 50 μl of competent cells. Plasmid or ligation product can be added directly into the transformation tubes for convenience. C2523I is packaged with 6 tubes, each containing 200 μl of competent cells. The tubes should be thawed on ice and 50 μl of cells transferred into new tubes prior to transformation. Each tube contains enough cells for 4 transformations with the benefit of reducing the cost of each transformation. If you perform 3 or 4 transformations at a time, using C2523I is cost effective. Refreezing the competent cells after thawing is not recommended since it will significantly reduce transformation efficiencies.