If the "practice mode" version is non-progression and non-loot, it's a good idea...
Non-progression also implies that you enter from the start every time you enter, having to clear trash all the way to boss every time.
And clearing one turn in "practice mode" means you can't enter next turn without clear it for real during the current progression week.

No progression, no loot, no cutscenes or any story... Just enter and learn from people that have cleared it. Assuming that people would actually help teach it since they get no loot for doing it.