Which Meluna are you interested in? They have many different cup configurations - firm, soft, ring, traditional stem, ball stem, etc.
I have a Meluna cup but it's from over 10 years ago and so it's a slightly different design from what's available today. It's basically their mini with a ball stem. I never had any issues with opening it, as it was a medium firmness. If you get their soft cup or a larger size, you may have to work a bit more to get it to open fully.
I liked it for my light days. I stopped using it because it developed a tear on the inside right at the bottom. It was a very sharp and pointy bottom, and I flipped the cup inside out to clean the bottom better, but that just stressed the point until it tore. Not sure if they still make the mini with such a pointy inside. It definitely wouldn't be an issue with their larger cups.