Only valid during the two summer months. It's a rather weak simile of the German Deutschlandticket (now 58 euro/month but valid all day on bus/tram/metro and local/regional trains, but not on long distance trains, in a much larger country).
It started out as an idea to introduce the same concept as the Deutschlandticket in NL. But the government has a budget deficit and the national railway company expected a capacity issue during peak hours. As a result the ticket is only valid in off-peak hours and the low price is only for 2 months.
