The future gadget is a full-fledged time machine, albeit it is still incomplete and, as a result, is only capable of allowing the user to travel backwards in time, as opposed to the time machine developed by SERN, which enabled time travel in both directions. There is one exception to this, however. In the Beta worldline, the time machine is able to travel both forwards and backwards in time, but requires a large quantity of fuel in order to travel.
At first, the time machine plays a backseat role, only being referenced occasionally. This changes in the sixth chapter of the visual novel, where the fact that the time machine is a future gadget is revealed. It is also revealed in chapter six that Hashida left the time machine to his daughter, Amane Suzuha, so that she could travel back in time and overthrow SERN's dystopia.
At the beta world line, it is completed to stop World War 3 and to enter "The Steins;Gate" aka divergence 1.048596% where everyone survives and neither the SERN Dystopia or World War 3 takes place.