Search entropia life for discoveries of golden key parts, it will show which instance drops what. Key 1 drops gears, which have quite a nice MU, third in line behind outer rings and codex chambers.
Key loot TT return is typically 75-80%. There is the chance to loot special items like arkoins and gears (in lvl1). I should say though... gears are quite rare (that's why their markup is so high in spite of being a "low level part") so you may have to run a large number of instances before finding any.