The invisible range is a more luxurious fabric with heat bonded
seams ( done by hand) that are not only very comfortable but give a
very nice “no show” look. The fabric and the methodology is more
expensive.
The Seamless is knitted all in one piece including the waist
and leg elastication – it’s different but not in the same class as the
invisible. Its called seamless as it is knitted in one flat piece – but
with a brief ( as opposed to a T shirt type top)  there is actually a
seam where it is joined together between the legs – other than that
there are no other “joins” viz. on the waist and on the sides.