Write rate is unstable

The write rate varies between the advertised 20 MB / s and random, much smaller values, down to the 1MB / s range. Read rate is not stable at 35MB / s, but falls sometimes to 25MB / s, ie on average worse than for example in the 8GB version.
This connector also comes just scratching and bucking in the bush, not smooth like normal USB connectors. I fear that I allow the USB socket in the laptop ruin me permanently.
Outwardly very small and elegant, but that is not enough for a good product.