My Grandmother died in 1981, when I was 10, so though I remember her, I knew very little about her. Towards the end of last year my cousin came to stay, and with her a photocopied and bound copy of my grandmothers memoirs. I have known she had written it for years, but has always been kept as something of a family treasure, and I never got the chance to read it during hectic family get togethers.
She was born in 1895, and to suddenly have such a close insight to losing close family members to the first war brought home the terror that that war was. For me the most moving part was the stuff written about my mother and my aunt. Mum died in 1992 so to read a Mothers perspective on my mum was very special to me, giving me greater confidence in my own memories of my mum, but also a new respect for how she handled problems I never knew she faced.
So what I am trying to say is DO IT! but ask questions to which you already know the answers, the recordings will not just be for you, but also your kids. I suggest you sit down with him some time before you do the recordings and ask him what he wants to talk about, and what he thinks are the interesting parts of his life.