No soldering is necessary to use that kit. It includes a solderless breadboard that allows you to make connections to all of the included components by simply poking them into the holes in the breadboard. It also has jumper wires that can be plugged into the Arduino Uno board and the breadboard:
I don't know whether it's the best starter kit. It does have the advantage of supporting the work Arduino does. Regardless of whose kit you buy, your nephew will be using Arduino's free software and documentation.
Al alternative would be to put together your own kit. I would lean toward an Arduino Nano and one of the larger 830 point breadboards. The Nano plugs right into the breadboard, which is quite convenient. The jumper wires are essential and I would recommend getting the male-male, male-female, and female-female to ensure all possible wiring configurations are supported. After that, you can just buy whatever other components you think your nephew would enjoy. Maybe throw in one of those <$4 multimeters while you're at it. If you want to support Arduino, you could buy an official Nano and then save money on the rest of the components by buying them cheap from China (which is likely where all the parts in the official kit other than the Uno are made anyway). Of course, you lose out on the project book that comes with the official starter kit. I'm not sure how much value that has as I've never seen it. There is already a tremendous number of tutorials and information available free online.