

I use them everyday. I work in logistics. Trick number one is to have special tape that isn’t as loud when unrolling it.
Tip number two is just use your finger to put the first bit on, hold it with the finger and do the rest. At the end, push the top part against the box to make the knife cut the tape.
Wipe over the tape with your finger if needed, some tapes and kinds of carton don’t have much holding power. If you move your fingers over the tape, you’ll heat up the glue and it will stick better.
In my honest amateur opinion karate seems more about both strikes and kicks, while the other one is basically almost all kicks.
Either would be fine I suppose. Also depends what you want to get out of it. Both sports will make a kid tired, both will have some sort of discipline build in.
Why decide now? Try both, see what the kid likes better. At a young age it is mostly about who their friends are and what they are doing anyway.