The Mark II droids were designed to look humanoid in appearance than the earlier Mark I models, which were smaller and quadrupedal. The Mark II droid was equipped with a more powerful Mining laser than the earlier Mark I droids.
Mark II mining droids were used extensively during the Old Republic era. Many of the droids were used at the Peragus Mining Facility for the mining and extraction of fuel which was to be sold offworld. In 3951 BBY several of these droids were reprogrammed by an HK-50 unit to attack and kill the miners in the Peragus Facility. These were destroyed by the Harbinger when the ship, commandeered by Darth Sion fired on the Ebon Hawk and missed, destroying Peragus II.
Certain promotional shots seem to show an earlier concept of what the mining droid Mark II looked like. This concept can still be found in the game files.