This week I was able to practice already completed lessons on the web, accessed through chrome on the smartphone.
I have also been able to practice already-completed lessons on the app for weeks -- using app on Android.
You don't lose hearts on the web, so it might make me opt for the web to use practice.
On the other hand, there are no English tiles on the web, so there's more of a chance of typing an English translation that Duo won't accept on the web.
Plus I also get the feeling that there's not the breadth of questions available versus, say, when you get the skill on general practice or like you used to through the old checkpoint practices.
Up to ten XP for a completed practice. Five plus an up to five bonus.
Anyway, it's this way for en-fr on the android. I'm assuming this ability to practice already completed lessons is going out to other platforms & languages.