Klein Star

The Klein Star is one of the most powerful items, and without a doubt the most expensive item in Equivalent Exchange.
When you place two Level 1 Klein Stars in your inventory, they combine to make a level 2. Every time you place a Klein Star Level 1 in your inventory while another Klein Star below level 5 is in your inventory, the Level 1 will be eaten to upgrade your existing Klein Star.
Level 1) Makes all power item functions that consume ONLY redstone free, except for the Soul Stone. Lowers cost of DM Sword, Hyperkinetic Lens, and Catalytic Lens so that level 1 is free. Doubles the fuel efficiency of everything else.
Level 2) Allows the Klein Star to be used in any furnace as if it were a piece of coal, infinitely. Further lowers DM Sword and Lens' costs. Triples other fuel efficiencies.
Level 3) All fuel rates for power items are quadrupled. Consumption rates further decreased.
Level 4) All fuel rates for power items are quintupled. Consumption rates *almost* free.
Level 5) Everything that uses redstone or glowstone dust except the Soul Stone is free to use.
It can also be used inside of a DM Locus, infinitely. The DM Locus will also receive a 100% speed bonus.
NOTE: The Klein Star got a mega-nerf (cost increased 4-fold) in the 4.13 release
This is mainly due to the amount of people explaining how easy it was for them to get it.