Hi, I use a "Gossen Lunasix F" and have done for many years.
Very reliable and accurate. They will measure ambient light reflective or incident and are sensitive enough to measure moonlight.
They will also measure flash reflective or incident, either singular flash or accumulative.
Although they are quite old they are very very good meters and there are several of them available on ebay at the moment. You should be able to pick a good one up for about £65.00.
Hope this helps.