These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The Flash, a secret unlockable gunpod, is quite simply the best weapon in the game. And once you get it, you can select it as a starter gunpod in a new game.
The Grenade and Python also qualify, both arguably the most powerful gunpods in terms of damage per hit. However, the Python is shot out in a rather randomly arranged string, making it hard to hit enemies and thus Awesome but Impractical.
No Export for You: PSN-wise, that is. While Einhander was released to North American markets in 1998, it has yet to see a PS One Classics rerelease on the NA PlayStation Store. Naturally, it has been available on Japan's PlayStation Store since 2008.
Made slightly less bad because the PS3/PSP/PSV are region free, and the fact that the game is largely already in English.