I've had my merula for 2 years already. At first I was very satisfied with it and it worked great... I even posted a detailed review on it! But my opinion changed a bit. I've realised I rarely use it, because I almost always still use my lunette model 1.
I bought the merula in hope to have higher capacity for busy days. However, when I overflow my merula, and pour the blood into lunette to compare the level at which they overflow on my heaviest day, I realise that merula collects either the same amount or less blood with my particular anatomy. I have a cervix that hangs very low, however, the length of my vaginal canal (so, the fornices) are relatively long(er)
While Lunette, has smaller diameter and under less suction (because of the holes), when it fills up and gets heavier, it slides more towards opening, allowing also allowing for additional space in the cup which the cervix occupied beforehand.
In merula however (and this, I think is because of strong suction), the cup does not descend ever, and engulfs much of the cervix, therefore occupying more of its capacity.
Merula is a perfect cup for people with low cervix and a shorter vaginal canal, I guess. I really wanted to like it in the long-term... but I'm my case, I don't get the benefit of the capacity, therefore I don't think I'll ever fully be satisfied with this cup :(
If anyone has any advice for me though, I'd be happy to hear.