This is my first purchase of packing underwear and I am so pleased with them! (I read a lot of reviews/descriptions of other packing underwear and I think I made a wise choice purchasing this particular brand/style).
I read all the reviews for this particular underwear and agree with these sentiments: my packer stays in place in these packing briefs (I'm non-binary and I wear a small Mr. Softie soft packer). I also agree that one should buy a much larger size of this underwear than they think they need. I'm 5'2" tall and weigh 136 lbs. My thighs are not small (about 25" in diameter at the same point of the leg-hole seam for these packing briefs). I normally buy a size medium in "men's" briefs and/or bikini briefs (Hanes or Jockey brand) which is a like a 31-33" waist. After reading the reviews/recommendations on sizing for Jockmail Packing Briefs, I decided to err on the side of caution and get the XL (2 sizes above my regular size). I'm glad I did! The XL size fits my thighs comfortably and the seam of the leg-hole does not dig into my thighs. The waistband is not as snug as I'd like given this larger size but it is secure enough. (It's not like the waistband is loose or falling down. These Packing Briefs also passed the "accidentally showing butt-crack test" and does not show any butt-crack if I squat and bend forward. At the same time, they are not high-waisted. So, for me, this is perfectly where I like the waistband of my underwear to be.
I would recommend these Jockmail Packing Briefs if your bodily dimensions are close to mine, slightly bigger, or definitely smaller. I plan on buying more of this same underwear in the future.