I used the saws for the foam pumpkins until last year.
I now use only a hot blade to melt the foam and I can't see doing it any other way. I have carved some very complicated things (the last supper took me about 7 hours over a 3 day period) and I would not have been able to do it with any other tool.
I also cut the bottom out but only large enough to put the low wattage flicker light in since a live fire is out of the question.
If you have not tried the hot knife, I recommend it! You will be VERY happy you switched.
My avitar was one I carved with the hot knife on a medium sized foam pumpkin (fun-kin).
This one is with a bright white light so the detail is more pronounced.
This is the flicker light which makes it a little dimmer, but the detail looks better in person.