By default the MJX X600 comes installed with copper bushings to guide the propellor axles.
(bearing left and bushing still in the motor pod right)
On Ebay or AliExpress you can find bearings that fit into the motorpods for a small amount of money. Each motorpod has 2 bushings so you need a total of 12 bearings and the size to look for is 3x6x2 mm.
(comparison of bearing and bushing)
Opening the motorpods can be a bit tricky at first. Also you have to do 6 of them and each pod contains 6 screws (7 with the propellor screw included).
First you have to unscrew the propellor screw. These screws are often dull. To get them out you have to guide them by wedging a knife blade behind them while unscrewing the screw. Having three hands is preferable.
When the prop is off the next five screws are easy and straightforward. The last screw is located inside the pod and you can see it looking down next to the motor.
The old bushing are held in place by friction and some goo. Gently pry them out with a screwdriver and push in the new bearing.
After installing the bearings I notice a slight less rattling noise from the motorpods during flight. There seems to be less play in the axles as well. Time will tell how well those bearings will hold though. They could be a bit more susceptible to dirt than the stock bushings though.