User blog comment:New Guy/Final Getsuga Tenshou and Quincy Final Form/@comment-44061-20101014173451

As Mohrpheus stated they are two different things. Yes they both are the pinnacle of power for their respective users but thats where the similarities end. The Quincy Letz Stil is brought upon by artificial means. By using and mastering the Sanrei Glove and then removing it you initiate the Letz Stil. But after its use the spiritual awareness still remains even with the loss of the qunicy powers, then we find it was possible to regain the lost powers as the quincy have a technique to use in the event of this type of situation.

Saigo no Getsuga Tensho is purely a learned technique natural to Ichigo's powers and upon its use Ichigo lost not shinigami powers and his spiritual awareness. If his father is any indication there maybe no way to get the powers back except if they choose to return after a certain amount of time. This is under the assumption that his father did nothing to get his powers back but wait. In any case it took 20 years to do so.