These briquettes are made from waste bark sourced from Pine and Spruce trees and then dried to under 10% moisture content. The bark is designed by nature not to burn, hence the long, slow burn characteristics of dry bark.
It requires more heat to dry bark down to under 10% moisture than it does to dry virgin wood, hence the extra cost. However, the extra long-burn characteristics justify the cost for many.
The Wind down the air and these are sure to stay in overnight. That is not to say you can come down next morning, give them a poke and they burst into flames, rather that there is still a good warmth in the stove and a glow from the ashes. Place some Starter Cobs or Kindling Discs in the members, open up the air flow and it will soon burst into life.
Bear in mind that back does produce extra ash, which is a double edged sword; more ash creates a bigger heat store, but also more ash to dispose of the next day. However, it can go straight to the garden.
RUF refers to the type of machine used to manufacture these briquettes.