"I open the window."
I think the idea is that most people don't have japanese keyboard on their phone or computer, so they use this method to allow forming a sentence. Idealy you'd want people to write the sentence from scratch.
Asking people to use a japanese keyboard for phone would defeat the purpose though, if you try it, you'll see it works with english letters to form the syllables, and you got a toolbar to choose kanji, katakana and other suggestions, like auto correct. So if you want to learn to read, better stick with this first.
I think rather the idea is that it seems random, as some words are split while others aren't. It can help if you are pronouncing morae in your head while searching, which is effectively like typing here, but they aren't always split at that boundary. I think it may help some instances of parsing, and it does make sense for inflections, but I still think it's a bit unnecessary for vocabulary. Being able to recognize full strings of kana quickly is going to be more beneficial.
And as for a Japanese keyboard, that is going to depend entirely upon one's device. There are, naturally, kana-input keyboards available elsewhere if one's device offers only Roman input of Japanese, for some incomprehensible reason.
Auto-correct wouldn't be an issue, as other courses usually recommend getting their supporting keyboards. So far, Japanese is the only course I'm doing that does not require manual input. And getting Japanese flip-phone style/kana keyboards is quite easy.
So to be honest, I'm just surprised they don't have manual typing set up, but I assumed that is because it is new.