I dont agree with the latter! I find the SLR (30 degrees of hip flexion) to work in a wonderful manner. that's because ur emphasizing the quadriceps to work in that range (not more than 30 degrees because u'll be recruting the hip flexors then) thus strengthening them in that range which is a good thing to do since we all know that during heel strike of gait , there is around 30 degrees of hip flexion with the knee locked. So, yes its a functional exercise in a way!