Currently MTNL is currently handing out the Beetel B450TC1 modem cum WiFi
router to its customer who opt for wifi. This is a combined
ADSL modem+ cum wifi router. As you mentioned the rent is the same but there will be an additional one time installation charge (if I am not mistaken). You have three option
1) Go in for a 2 in 1 unit from MTNL & continue to pay monthly rent.
2) Buy your own ADSL modem+ cum wifi router (combined unit).
3) Buy only the wifi router so it can be used with your FTTH connection in future.
Regarding the range there are a lot of imponderables which can affect the range of a wifi unit & is very difficult to guess till one actually checks the signal strength on site.
If you want to go in for the (1) option you can just call 1500 & tell them they will call back to confirm, that’s it. They will do the rest.
For the (2) option you go ahead & buy the unit of your choice & install it, then return the MTNL piece to them.
For the (3) option you buy the unit of your choice & install it.