Both kits are spectrophotometric based and would require a wavelength of 340 nm for their performance. The choice between both is usually down to user preference.
Generally the benefit of the liquid ready kits are that the formulations are ready to use. There is no preparation of vials involved. Also within the assay then there are less components to be pipetted into the cuvette, therefore less room for error.
This is important if an accredited method is required. K-FRUGL is accredited as AOAC method 985.09, K-FRGLQR is not an accredited method.
The assay principle is the same for both kits.
The K-FRGLQR assay protocol does not give a "manual method" whilst this is possible to use for cuvette style assay you will need to multiple volumes by a factor of 10. No calculation is then given for manual assays. This kit is designed for autoanalysers and or microplates really.
If a manual method is required we recommend K-FRUGL.