In reply to BobHoliday:
This won't be very helpful, and I don't recommend this to anyone, but when we did the same itinerary around 20 years ago, we didn't take axes at all. We figured (at this time of year) the Mer de Glace didn't need axes as it was bare, and the Moine neither as it was about 5 minutes plod up buckets, and mush on the descent, with a good runout.
Crampons are needed if you're going up the Mer de Glace in the morning, but I've never used them for evening descents, but I would always take them.
Post edited at 12:05