How good is Giant's atx670? Please tell me in detail.

The 670 transmission system generally uses the TOURNEY TX system. Specifically, it is the TX-50 rear derailleur (smartcage guide wheel plate and 15T large guide wheel), the 42T swing-down positioning front derailleur, and 7speed MEGARANCE twist flywheel and 2007 TOURNEY shifter. It depends on your requirements for the car. If you have enough budget, it is not recommended to buy an ATX-6 car. Because it uses a twist flywheel, if you want to upgrade to 8 or 9 speed, you need to replace the entire wheel set. If you are not too pursuing performance or think that the ATX-6 series of cars is enough, I suggest you buy an ATX680 or ATX690. These two cars use quick-release hubs, and the rear derailleurs use ALUTS series rear derailleurs. ALUTS is a universal product for 7- and 8-year-olds, and its performance is much better than TX-50. (ALUTS refers to the SHIMANO ALUTS series, TX refers to the SHIMANO TOURNEY TX series)