Reformation is known for being a sustainable, ethical, and an elegant brand. Having bought a dress from them myself, I can say with confidence that their clothes are high quality, true to size, and as far as I can see, sustainable. Due to these factors, their clothes are of course on the slightly more expensive side, but it is worth it if you're looking to get some long lasting pieces.
The shipping took a while (10-15 days), most likely due to me ordering the dress around christmas, which is a chaotic time for shipping. The sizing only goes up to about 12 on dresses, and while there is variety on dresses and their patterns/colors, the actual styles of the dresses can be quite similar, usually differing in texture or cut a little bit. Reformation is definitely one of those brands where you just know that it's "the reformation dress" when you wear it or see it.
The annoying thing is that the website will not only show the same dress in multiple colors on one tab, but it'll show the same dress multiple times in those different colors/patterns, which means that it's a bit more chaotic to shop for clothes if you don't have anything specific in mind to shop for. Also, different color or pattern options will cost more than others of the exact same dress, which doesn't really make sense. My overall experience though, was great, and even as an hourglass figure, I was able to fit into my usual size S (there are measurements for each garment on their website)