A sleeping mattress’ main functions are to both provide insulation from the cold floor (where your nice expensive down gets crushed to a few millimetres) and provide comfort from the hardness of the ground - allowing your pointy bits to be cushioned.
The Balloonbed provides very good cushioing and won't impact significantly on the size and weight of your rucksack. The balloons within the Balloonbed system are very comfortable as they are elastic and stretch easily to absorb those pointy bits of your body.
Comfort v Competitiveness
We are not all the same. Everyone competing in a Mountain Marathon will have different abilities and aspirations. Most agree though that carrying less gear will enable them to perform better. And we all want to perform better… it is a competition after all! Like most areas of our lives, you have to make compromises in an MM. Do you want to have an incredibly light and skinny sack and be faster or do you want to be comfortable at overnight camp? You really can’t have it both ways, so you’ll have to go somewhere down the middle road - everyone will choose a level of comfort they are happy with and as consequence a sack weight that they feel is acceptable.
The items that make a big impact on sack weight and volume and only get used at overnight are: Tent, sleeping bag, sleeping mattress. The size and weight of all these items will affect your comfort at overnight camp.
You can spend a lot of money going light with a sub kilo tent. Down sleeping bags can also set you back a bit ... but luckily for you, Balloonbed provides a lot of comfort for a relatively small outlay.