Stable, accurate temperature readings are critical to 3d print quality and key to this is good thermal conductivity (as Atom) says from the heat block to the thermistor. Having it is semi contacting the heat block with an air gap around it and it able to move during print will lead to inaccurate temparature readings and fluctuating hot end temperatures. These need to be secured with potting compound, viscous thermal paste or such like.
I would suggest either fix at factory or at least supply some compound with future printers to allow end user to secure