Hi, I currently have unlimited hotspot plan from Maxis. I'm trying to put a sim card into a 4G/5G modem so that I get WiFi at home without draining my phone battery. A search in online shopping sites showed many unlocked/modified modems. May I know if there is any disadvantage of these unlocked/modified modems compared to the original ones?
Will there be speed and stability issue especially?

They totally know you are using modified devices, and at any time they could decide its the end of it - and blacklist your device or worse, your account. And they have every rights to do so.

YES would block your sim card if you use modified device, so...

The telcos are getting smarter and they are blocking IMEI of modems now. Once blocked, it will never work with the telco again.

Enjoy it while it lasts.