Also on the downsides, I don't know for other languages but in French the words are NOT common words and a good half of them would require a dictionary for a native speaker, making the address system useless.
The center of Vienna is "decays.jump.graver" (if those are simple words is questionable).
But when I switch to German the same block becomes "fahrende.hügeligen.ansprüche" (driving, hilly, demands). So the words I get by default are again just random strings for someone who doesn't speak German)
And even someone who speaks German may get the inflection of the words wrong and end up in "fahren.hügelig.ansprüche", "fahrend.hügelige.ansprüche" or any other permutation of the many ways the same word could be written in another context.
And worst of all, all those permutations exist and map to other locations somewhere on earth.
Personally I want a public domain list of 2^k distinct words of distinct and unambiguous enough meanings, that are then translated to many other languages and evaluated for the same criteria (in reality, such system will be required to begin with as many languages as possible). My best guess is that k=10 is possible with a lot of efforts.
To be honest they did give a thought about this, as apparently close sounding words are supposed to map to places that are far apart.
It makes sense, as you should at least know if you're looking for a place in Austria or Burkina-Faso, but it also means that if you heard the words wrong then you depend on their algorithm to find a slightly different-sounding address that is the one you were looking for, instead of a more intuitive system where you could just around because if it sounded the same then it should be closer.
And since the word list is proprietary, you really entirely depend on them. Their website shows three different suggestions, the one you typed and two close sounding ones.
Tough luck if you typed "duper.listons.égalisons" and the actual address was "duper.listons.égalisation", you won't get it in the suggestions.
The words in different languages also aren't translations, they are completely different, which adds a layer of confusion. I really don't see this going anywhere.
Edit: A few examples taken randomly of mostly unused words in French (require a dictionary for a good 90% of native speakers): Volute, redise, dépiler, rapière, ânier, putatif, toison. All of that is in the center of Paris, and it took me 5 mins to find them, there's probably hundreds of rare words.
This is completely absurd.
Do you need to? If you don't speak the appropriate language you won't know the meaning of the words for any place. That doesn't make it any less useful so long as you can pronounce them.
For one we have plenty of homphones. Is it saut, seau, sôt sceau ?
Then if you do not know a word, say châtière, it can become chattière.
So only homophonically unique words and well known ones should be used