I do believe that this pop-up language learning style is great, yet there are some issues with it tampering with your writing.
As a content writer, I realized I had trouble writing whilst listening to music that has lyrics. The song's words and thoughts mix with the ones I'm trying to come up with. So I stick to instrumental music. Yet there are even studies that suggest listening to music of all types hinders writing. Other examples. Basically, it's quite hard to do two language processing activities at the same time.
It will be hard, possibly frustrating, writing solid, advanced, longish sentences, keeping the train of thought, while a pop up changes the language of a word you just wrote. It will certainly prolong the writing process.
I've been using Toucan, which has a very similar principle, for a language I already know quite a bit (Spanish), but it still gets in the way of a thought process and when the subject matter is complex, I have to pause the extension. Even though I'm only digesting information, not even creating. And even though I already know a bunch of the words I get shown.
So maybe the solution is to only use the app when you are writing every day stuff like communicating with friends. Maybe there's a different solution for this issue?