Serotta Ottrott ST, Titus RX100, Seven Sola 29er HT in the works
Roller resistance increases as the circumference of the roller decreases. You can also increase resistance with an integrated fan unit.
How much resistance? I don't have a measurement to contrast/compare to trainers. As a rule of thumb, trainers are the better bet for dialing in a higher resistance for interval training where rollers are the choice for developing form and endurance.