As they are filled with 100% Pure Long Fiber Mulberry Silk, they both offer a very breathable covering compared to down or polyester filled duvets.
The difference between the two comes down to the climate that you live in. We live in Chicago and the all-season is perfect for us all year round. There may be some nights of extreme cold temperatures, whereby we need an extra blanket and vice versa on exceptionally hot nights we may pull back the duvet insert.
If you live in an exceptionally hot climate all year round or sleep noticeably hot, the summer weight would be a suitable option. Otherwise, the all-season is perfect for most climates with a variation of seasons.