It wouldn't be that big of a deal if the cops just searched his computers/hard drives, concluded he wasn't involved in the child porn, and gave him his hardware back with a "sorry for the inconvenience".
But it doesn't happen that way. If Austria is anything like the US, he will never get his property back. So it isn't a temporary inconvenience, he's been punished permanently before even getting a trial. And when this case does go to court, even if he wins he'll be very lucky to get his property back.
I absolutely agree that seizure rules need to be SEVERELY reformed, and that the way that seizures are currently carried out is unacceptable. However, I don't think that it fundamentally changes the situation in this case. Until seizure rules end up getting reformed, law enforcement plays with the hand they've got, not the hand we wish they had. If the choices are between "permanent" seizure or just walking away from a suspect, they'll go for the seizure every time.
Seizing equipment for at least some period of time is absolutely necessary for any kind of forensic examination. It's part of the cost of having laws, and the imperfect nature of human justice means that that cost will occasionally be paid by the innocent as well as the guilty. I agree that that cost should be lower so that innocent people are not unduly punished, but there will always be a cost.
But it doesn't happen that way. If Austria is anything like the US, he will never get his property back. So it isn't a temporary inconvenience, he's been punished permanently before even getting a trial. And when this case does go to court, even if he wins he'll be very lucky to get his property back.