A seamless thong is bonded rather than stitched, so there is no edge to press a line into what is over it. Under a fitted skirt that settles it. Lace does not leave a line either, but it is a texture with holes in it, so under a fine knit it can print as a faint pattern instead of nothing. The trade going the other way is fit: the lace one is a single stretch size that finds the body, and the seamless one is sized and has to be right. So if you are reliably between two sizes, or the day is warm, the lace is the one that behaves. If the outer layer is thin and close, the seamless is.
Invisible and seamless are not the same claim
Seamless describes construction: whether the edges are bonded or stitched. Invisible is a result, and lace reaches it by a different route, since it has no edge to print in the first place. What decides it is the fabric over the top. A heavy jean does not care either way; a fine jersey shows a texture as readily as it shows a line.
One size is a real property here, not a marketing line
The listing fits one size to US 4-14, a range six sizes would normally cover, and the house has sold it that way for thirty years rather than sizing it. That is what makes it the safer thing to buy without trying on -- and it is also the limit: a fuller figure wants the house's own plus cut, which is a separate listing rather than a larger version of this one.
