I recently bought the L-508, mainly for use with medium and large format systems. I think this is great meter if you are going to have one handheld meter. It makes compromises in many areas but you don't have anything else that I know of with these capabilities. The compromises - no viewfinder readout when using the spot mode, less low light sensitivity in reflected mode compared to a L-778, limited averaging capability, etc. On the plus side, incident, reflected variable angle spot and flash meter in one package. With an F5 do you need it? Well, I use mine with my N90s anytime I have concerns about highly reflective settings (read snow here in Minnesota). I prefer the L-508 spot capabilities over switching the N90s to spot mode. It's also great to have a flash meter to evaluate flash shots, especially if using multiple flash set-ups. Do you need a handheld meter if you have built in meters as good as the F5 or N90s? I know it has made the difference between great shots and okay shots for me more than once. A handheld meter also forces you to evaluate each exposure more carefully, the same benefit as using a MF or LF camera. You don't lean on the shutter release until you have thought the shot through carefully.
