That you get to constantly see the dirt in the transparent front, I do not think is optimal. Normally, one notices that the teat is full to the declining performance because it does not need a clear look.
Another drawback: the power button, which can not be locked. You have all the time draufhalten thumbs, which, although in the long run leads to strong thumb muscles, but complicates the handling of the device while sucking.
That's it so far - supplements if necessary.