Question About SIFY WLAN Signal


Now Visible in NCR ;)
Airtel Broadband + 4G and Voda 4G
I am having problems living with BSNL again, and apart from other options I am looking at getting a SIFY connection as backup.

The cable guy who operates SIFY says there are 2 type connection is available.
1). a wireless device would be fixed on roof top and wire from this device will come into computer's LAN CARD. cost Rs.2-3k

2). A Cat5 cable from their HUB which is on every lane in my locality to comp.
installation cost Rs.1k

apart from this I am seeing SIFY signals on my laptop, so is it possible i buy a connection and still connect to internet from SIFY.

what i don't understand is when the signal is already available why do we need stupid roof top equipment or cat5 cable to be used.

Please see the screenshot the SIFY signal is very prominently visible all over my area.

Any suggestions