Market price is always up to date
Pörssi is an energy contract what follows the energy market price (so called spot price). The per kWh price varies hourly according to the current market price in the Nor Pool energy exchange and its price for the Finnish market.
With this contract type, you can optimize your energy consuption and make use of the low market prices. The downside is the risk of price volatility. While prices can drop low, they can also climb high.
With Pörssi, you don't commit to long contract terms. You can terminate the contract with a 14-day notice.