With a more powerful force field, a full set is able to deflect 100% of incoming damage, ranging from skeleton arrows to the full force of a nuclear blast. Each piece of armor can store up to 1 million EU, therefore, it can last a very long time before needing a recharge; however, you can only charge them in an MFS Unit. In addition to that, a full set grants you several passive and active abilities, by keeping your hunger and oxygen meters full, protecting you from poison and fire, reducing fall damage, and allowing you to sprint 3x as fast and jump up to 9 blocks high (a partial set will only grant the abilities tied to the pieces you are wearing - speed from the leggings; jump from the boots; oxygen, poison, and hunger from the helmet; fire from the bodyarmor).
The speed and jump boosts are activated by holding CTRL. However, all these abilities will also drain the energy of the suit over time, requiring more frequent recharging.
The Quantum Suit has a special weakness against the Nano Saber, having its energy reserves depleted and being destroyed in only a few hits.