Well, I'd destroy it. Be careful what you wish for. Hitler is killed in the early 1920s. In 1935, following a military coup in 1933, a right wing, authoritarian regime is imposed. With the aid of all the scientists who did not have to flee, Germany develops a nuclear bomb and easily defeats Russia. A much more ruthless version of the EU is imposed on Europe. Following the failure of the UK to come out of the 1930s slump it finally becomes a client state of Germany.
What device developed in the last 20 years would you not miss?