Sounds like this device acts like a semi permanent cache. If it can store files that are read alot on it, it would be a winner, but not for 50$. So, the OS files that are read the most often, the game that you launch most often, would be stored on this device seamlessly. Next time you boot, it's still there (unlike a RAM substitute) and you'll boot up quickly and launch your game quickly, everytime.
A true RAM cache or HDD cache doesn't work this way as it still has to read it off the HDD every time to store it in the cache for use.