Well, the video that a member from Germany who has recently purchased one, showed that the trigger needs to be fully released to re-set.
The trigger pull is LONG and looks in no way like the pull of the PPQ or P99AS in single action.
If you don't retract the slide ALL THE WAY to the rear of its travel, it will not cock the striker, unlike the PPQ and P99AS which will cock the striker within about a quarter of an inch of travel, so it looks like you could chamber a round and if you didn't FULLY retract the slide, the gun would not be cocked and it would not fire.
Also, his BRAND NEW in the box straight from Umarex/Walther pistol is a mess. It looks like it had a lot of rounds put down the pipe.
Go over to the Walther Forums and have a look around, that would be better than anything I can tell you.
This isn't an economical HK P7, don't even go there. If it works, it will be nothing but an entry level gun for beginners.
If it works.