The sizing chart was spot-on, and swapping these in took about ten seconds—no fighting with stiff plastic. The fit is snug enough that I get good suction without any pinching, which makes a huge difference during a long workday.
Ordered the size up since my flange fit was off and this insert fixed the gap immediately, no more slipping mid-pump. It clicks in securely and the silicone holds its shape even after a few hot-water washes, which is exactly what I needed for a backup part.
The soft silicone grips the flange edge so snugly that I stopped worrying about leaks mid-pump, and having just the one insert to swap out is honestly all I needed since the other size still fits fine. It clicks into place in under five seconds, which makes my early-morning sessions way less fiddly