Like I said, if you can use your own modem. You certainly should. But I totally get that in some countries, some users do not have that option(which is unfortunate).Also US specific, I believe. Is it common in the US to pay modem/router rental fees?
To answer your question, yes I’m going to say that it is okay extremely common in the USA.
Most households don’t even realize that they have a choice so they pay their cable ISP equipment fees as part of their monthly bill for the use of their ISP’s router-cable modem unit.