[Off Topic] Do you have the liberty to update/upgrade your router's firmware ?

During the last 10 years I have used 3 kinds of internet connection namely adsl, cable & 4G. I was using two separate Dlink routers for both adsl & cable & an ISP supplied router for 4G. All this time I was using the firmware which came with the routers. I tried installing DD-WRT but non of the routers were supported. Despite the fact that it was a security issue I was compelled to use the routers without updating the firmware.

What kind of routers do you use ?
Do you update/upgrade the firmware?
Have you used DD-WRT or any other open source firmware ?