We also did Drancy. We took the shuttle bus out and ended up walking back to the metro and taking the metro back. The tour (only in French) was very moving. Don't skip the museum inside with all the documentation. It is a bit creepy that people are still living in these buildings today (public housing). Well worth doing especially if you have not been to any of the actual concentration camps in Europe but do the Shoah Museum in Paris first. If you have visited the any of the camps, you will find it interesting but a bit sanitized in comparison.
Tip: if you are comfortable with the Paris metro, take it instead of the bus only because Sunday Paris traffic is terrible and the metro is faster. Use your phone to get to the museum. It was a nice walk (about 30 minutes) through the neighborhoods. Perfectly safe.