The water meter cost something between 20 and 25€, I replaced it myself and the sealing was, to my knowledge, around 50€.
Our outdoor water demand has been quite different in recent years. Some years it was about 30m³, but in one dry year it went almost up to 80m³, if I remember correctly.
So you already save by the end of the first year and then for the remaining 4. For those who have a large pool, it is likely to be even more worthwhile.
The risk I see in our case is that due to climate change it will eventually be forbidden to spray the lawn with drinking water. Compared to all of Germany, we get significantly less rain. Then you start building a cistern, which would have paid off much earlier if built in time.