They seem well made and have plenty of space. Only time and use will show whether—and what—they can really withstand. They’re made of PVC, which means they’re completely waterproof, and all the seams are glued (this is a vulnerable point with PVC). For that very reason, be very careful to keep them away from the exhaust—far away! ...very far away!
I had a little trouble fitting them because, partly due to the exhaust, the mounts (the rails) are quite far apart, so the two wide flaps (?) wings (?) can’t overlap and be fastened together with the Velcro (see photo). They’re supported only by the straps. The ideal distance between the mounts, including the “hump” of the seat, would be 50–55 cm.
They also require a little ingenuity and perhaps a few small modifications to the remaining straps to secure them so they don’t move back and forth.
Overall, a good purchase, and any minor difficulties with fitting them are overshadowed by their very good price.
P.S. The package also includes two semi-rigid panels, which are intended to keep the inside of each pannier open to its full capacity and help it hold its shape better, as well as make it easier to pack. They’re not the easiest things to install: there are two inverted pockets on the inside walls of the pannier, and with quite a bit of effort you have to insert the two ends of the panel into them, then spread it out (also with effort) across the entire bottom of the pannier so that a wide Velcro strap can wrap around it.