The benefit versus running on the phone would be that it runs quite a bit faster, but also that it doesn't drain battery and you can use the phone for other stuff in the meantime. One could also run many simulations at once, if you want to e.g. compare different radiation levels on a substrate then they could all be uploaded and run in parallel.
1 euro might seem steep but it is the minimum in app payment. Cloud computing seems to be about 5 cent/cpu/hour. 5 hours is then 25 cent. For a 1 euro payment i guess there is like 25% vat, google takes 30% (they take this on the amount before vat in some countries

