The Time Helmet was built for Gabe to allow him to enter the future and purchase Front Mission 4 before it comes out. The item worked, and Gabe successfully entered the future, meeting his future self and doing a high-five with him.
If one such person uses a device and meets himself, time itself will smash and create reality shards, sending universes into a sea of untime. However, this was a temporal warning, as Gabe easily met himself without the universe being destroyed. He even high-fived himself. This could be seen as a pre-destination paradox, with Future Gabe knowing where the original Gabe would be at that specific time.