This has everything for those who really need to change, as I do now that the locker rooms at my pool are closed for renovations. Though the poncho covers the chest nicely, it has three snaps you can undo in case you need to see the garment you are fastening up top. The arm openings also have a snap you can undo to make the opening larger, so you can maneuver garments underneath. There are in addition faux pockets behind the front kangaroo pocket so you can maneuver underneath when you don't need to see, like when you pull bottoms up.
I sized up to create enough room to move around underneath. I wear small or medium in streetwear and ordered the L/XL here after I found the S/M, though a good fit otherwise, too confining to change under quickly and efficiently.
Other perks: It's made of lightweight, soft, absorbent cotton terry. Though probably a little bulkier than some of the microfiber ponchos, it's easy enough to carry around and fits in my gym bag when rolled up. The generous hood has draw strings you can pull to create a closer fit, e.g., for warmth.