I've used this method quite successfully but you do have to be careful. Jenny demonstrates with 5" squares - so bias sides are no where near as long as they would be with 10" squares. It is a great way to make pinwheels for a baby quilt. I think you just need to stick to smaller squares.

I starch, then press (not iron) then cut.

I am making her quilt and after I sewed all around the edges and then made the cuts, I had to square the blocks to 6 or 6.5 inches can't remover which but that was the problem for me. I have found that layer cakes do not always have squares that are exactly 10". Because of the differences in the original squares, it threw them all off. Hope this helps.