Trained to build and/or destroy almost anything, the clone engineers are extremely useful and highly respected. They have also received extensive training in vehicle repair and maintenance allowing them to perform repairs on the battlefield.
This trooper has taken up a fallen brothers heavy repeating blaster, similar to modern light machine guns. The model seen here is a detached vehicle turret. The infantry model resembles the DC-15A blaster rifle although it is shorter to reduce weight but can be customised with longer barrels and bipods for increased accuracy.
Saw a weapon like that in a clone wars comic and thought it looked better than that gatling gun thing they use.