There are sources that indicate that it was used during the war even is those are rare.
At around 22:25 he addresses the operational history.
For me personaly there is a big diffrence between a certain thing just driving around in the aberdeen proving grounds somewhere across an entire ocean or it beeing directly tested in combat.
Thus the germans do have the a distict advantage when it comes to prototyps due to enjoying the home advantage of beeing on the defence and having to use what is available.