The Touristanbul tour by Turkish Airlines is actually quite well organized and many travelers use it during long layovers. They plan the schedule around flight times, so they’re usually very careful about getting everyone back to the airport on time.
For carry-on luggage, most people either leave it at the airport or keep it on the bus, depending on the tour and timing. The staff usually guide you through that when you register for the tour.
With a 9-hour layover, it should be manageable, and it’s a nice way to get a quick glimpse of Istanbul instead of waiting at the airport.