I originally used crimpers like those, and they suck-didly-ucked. I had as many bad crimps(if not more) as I did decent crimps. It would just flatten out the connectors too much(instead of curling over properly) and the pins wouldn't fit into the plastic housing. I bought an Engineer PA-21 crimper and I'm getting decent crimps >90% of the time. It's a two-step process, though - you have to crimp the conductor and then crimp the insulator, but ultimately it saves me time since I don't have to constantly redo crimps.

It’s very easy to crimp new connectors if you have the right tool. And you will find that a crimping tool and spare connectors comes in very handy with a 3D printer.

The connectors are JST-XH and you can find kits on Amazon. But don’t buy the kits with a crimper because those tools invariably suck.

The best inexpensive tool I’ve found is the IWISS IWS-2820M AWG 28-20 for around $20. If you want to treat yourself, the Engineer PA-21 is around $50 and by all accounts an excellent tool.

Whatever you do, don’t buy a tool that crimps both the conductor and the insulation at the same time. They rarely work well and break easily.