A couple of clarifications re this topic :
a/ For the non-francophones and to avoid any potential misunderstanding, la taule in French is a colloquial term meaning prison, in general, regardless of its status (civilian or military). In English, it would be translated as “the nick”.
b/ Officially, the distinction between arrêts simples and arrêts de rigueur does no longer exist or, more precisely, the notion of arrêts de rigueur has been discarded from the list of possible sanctions that can be given to a military personnel and only arrêts simples remain in force (article R4137-28 du Code de la Défense). It means in practice that a soldier who received x jours d'arrêts (days in ‘prison’), with a maximum of 40 per sentence will, as previously mentioned, execute his work normally, but will not be allowed to leave the barracks (or any other place designated by the hierarchy). That means no leave (and any leave that might have previously been granted is cancelled) and no quartier libre (short-term leave in the evening or during the week-ends). That's it. No more special place where soldiers are locked up, no more chores under the supervision of Service Général. Detention remains possible, but only if a soldier refuses to properly abide by the sanction rules (e.g. leaves the barracks unauthorized), in the case of very serious faults that could eventually result in a sentence in a civilian court, or if the soldier can be a danger to others. The jours d'arrêts belong to the lowest tier of possible sanctions. Depending on the gravity of the fault, there are higher possible sanctions, like for example demotion or contract termination.
Now... This is the law. Not sure how it is in reality applied in the Legion, who has a reputation of “interpreting” it its own way. Check the video below (quite old so, again, things might have change since).