I bought four pairs of Thinx about two years ago, what were then their most absorbent styles (I think things may have moved on a little since then). I think I bought them during the halcyon days of light periods just before the perimenopausal lightning struck. They failed within an hour.
The material is quite robust and leak-resistant but there is nothing to stop the blood from wicking round the side of the gusset, so I ended up with bloody patches about an inch either side of my trouser inseam.
They're also a little clammy, so if you have sensitive skin they may irritate it.
I now use reusable cotton pads, which I love, although the lack of plastic means that the wings are just as absorbant as the pad so blood can wick around them onto your thighs and trousers.