I bought this set last year for a trip and am happy with my purchase for the price. Please note that my review is mostly based on the larger suitcase...the smaller bag was a great size and worked perfectly for me but I feel like most people checking the reviews are probably more interested in the suitcase.
Since buying it I have taken it on a plane a total of six times, which is not really enough times for me to speak to the durability but I have not had any problems so far. I travel fairly infrequently so I didn't buy this with the intent to use it very often though. No problems with the zipper sticking/breaking despite having crammed it as full as possible. The retractable handle has held up well so far. Wheels still working fine. I mostly used it as a carry on but did have to check it a couple times just due to limited overhead space on the plane, not the size being too big. I got the light pink which was great because it made it super easy to locate at the luggage carousel, but since it is a light fabric it got pretty visibly dirty during it's checked journey. Not really a problem and expected due to the light color of the fabric, but something to keep in mind if checking the bag if you are considering the lighter color.
When using both pieces as my carry on luggage I did not have any problems with the size of either being too large, even when expanded (have taken it on American Airlines and Southwest flights). I like that the suitcase is expandable because I'm a notorious over-packer due to anxiety (I generally bring waaaaay too many clothes for my trip length so that I have them just in case) and each time I've used it I was able to fit everything I needed fairly easily.
My least favorite thing about this luggage is that the suitcase only has two wheels. It rolled well when tilted but if you are standing in a slow-moving line you can't just set it upright and roll it. That part is not so bad, just a bit annoying, but it did have some balance issues when standing it upright. I didn't have any trouble until I hooked the smaller bag onto the retractable handle on the top (the strap on the back of the small bag is perfect for this). The smaller bag sits perfectly on top of the suitcase, but it did make it very top heavy (or front heavy?) so that it would fall forward if I wasn't holding onto it. Again, not a big deal, just a little annoying. None of my friends who had bags with four wheels had a problem with their bags not being about to stand upright.
Overall, a good purchase considering the reasonable price. Next time when I upgrade I'll be looking for a bag with four swivel wheels instead, but in the meantime this does the job for a light traveler. I wouldn't expect it to hold up well for a heavy traveler however...not because I've noticed any visible damage yet but just based on the way it feels; not cheap exactly but it doesn't feel very durable.