[wolfbln]

it depends to what you compare it:
-> it's quite cheap for German prepaid prices.
Germany is a rather pricey EU country for mobile data.
50 GB at €80 means that 1 GB goes at €1.60 which is considered cheap here.

On the other hand, this offer is on the weakest network in Germany: o2/Telefónica.
There are currently very split opinions about this network provider.
It has a 4G availability of only 66% and mostly single digit Mbps download rates.
This means congestion in many inner cities and often no 4G coverage on the countryside.
But if you want to use it stationary in a well covered area, it may still be a good option.

Furthermore, more reliable 4G roaming in the EU/EEA is added without surcharges.
No FUP or any limit is applied so far by the provider which is a big plus for using it outside Germany.

Within the country, you get much better deals for postpaid contracts with 24 months of commitment.
Both Telekom and Vodafone sell real uncapped unlimited internet plans now for the same price in Germany (€80) on much better and faster networks.
And when you are still happy with o2/Telefonica. They sell unlimited data at €60 per month on similar contracts with a 2 years term.