Usually when I visit a new place I try to take a guided tour of some kind, just to let someone else do the navigating/driving while I thoroughly enjoy site-seeing. The tour we took on St. Maarten was -- I think -- the one you're considering. I loved being able to see the whole island, and I thought the tour was good overall, BUT... I think we had only about 20 minutes in Marigot. I loved it there, and didn't like feeling rushed to shop and see everything. Philipsburg, which we did explore on our own, just didn't compare, in my opinion.
If you do take the tour, you'll see some cool stuff and get info on the history of the island you probably wouldn't get otherwise. But if you enjoy open markets and handmade crafts, try to schedule some time in Marigot in addition to your tour stop. You won't be sorry!