No downside, it's just there to incentivize people to buy the product. They give the impression of a "good deal".
There are some legitimate reasons to have a separate keyboard. I use Keepass2Android's keyboard to enter passwords from Keepass. This way, there's direct access to the password database instead of copying passwords/usernames/other fields to the system clipboard.
Nice, I happen to be on vacation this month. Should have lots of time to build the factory