After seeing a few videos and reviews, I was skeptical about how much these would compress. While it's not as much as a spacebag or a ziplock with all the air pushed out, this is both better than I expected and a lot easier than the alternatives. I just finished packing for my first trip since purchasing (a week at a lake), and I was pleasantly surprised both at how much I could fit in these bags and how little space it took up. Here's what I packed: Size L (15x15): three pairs of swim trunks, short-sleeved rashguards and one long-sleeve rashguard with a hood, a pair of shorts, a polo shirt, a tank top, and a long-sleeved tshirt with a hood Size M (9x12): three oversized tshirts to sleep in, 2 pairs of cotton shorts, and a pair of pajama pants Slim (13x4): 2 pairs of socks and enough underwear to last the week. All of this took up literally less than one side of my clamshell-style carryon suitcase (9x14x20), which meant I had plenty of room to toss other stuff that normally would have been in my backpack into the suitcase - and anything that means trudging through the airport with less on my back makes me happy.
My partner saw me packing, saw how little space all my stuff took up, and decided he wanted a set too - which makes me happy it comes in so many colours.
There are two main downsides that keep me from rating it the full 5 stars. 1) They don't compress completely and can be a little difficult to zip around if you really pack them full. That said, a little nudging and fiddling and I got everything zipped. 2) I dislike that you have to buy them only as a full set and can't select additional ones based on the size you need, with the exception of the largest size. I would really like a few more medium-sized ones, but I would have to also buy either another large and small or another small and extra-small.
Overall, though, I'm very happy with these so far and look forward to using them on many trips in the future.