Their craze for the new invention is justa flash in the pan. The underlined phrase means -

A flash in the pan
English Meaning
1. Something that happened only once or for a short time and was not repeated:
Ex: Sadly, their success was just a flash in the pan.
2. Something that is interesting for only a short time:
Ex: The band was just a flash in the pan with one hit in 2003.

Bangla Meaning:
যে প্রচেষ্টা প্রায় শুরুতেই ব্যর্থতায় পর্যবসিত হয় বা চিরতরে খতম হয়ে যায়।

Source: Cambridge Dictionary and Accessible Dictionary by Bangla Academy.