ほんとに何のためにそれを買うのかよくわかりませんでした(笑)
香港では「5日間通話可能、1.5GBデータ通信可能なSIM(他にも種類あり)」なんかがコンビニで売っててフツーにお金を払うだけで買えるので、データ容量使いきったら即買い替えできるのがいいですね。

I really didn't understand very well why he was buying those. :-)

In Hong Kong, they sell SIM cards good for 5 days and 1.5GB of data communication (and they have other types too), which you can buy just by paying money as normal, so it's nice to be able to buy a replacement right away when you've used up your data capacity.