MFR is a very simple test and is useful in that a feel for polymer viscosity can be attained very quickly. Furthermore, the MFI value is totally indicative of polymer weight average molcular weight and, if using the ratio of two MFR values from dissimilar weights (flow rate ratio-FRR), its molecular weight distribution.
Visit the Fleming PTC (polymer testing & consultancy) website for more information on Melt Density Measure