Today i tried the custom firmware, my findings are as below

IDEA/Vodafone: there is a near by tower with good signal all i get is arounds 21 mpbs (download) most of the time, it broadcats only Band 3, tried 3,3 BANDA and BANDB. no CA     and only locks in BAND3. So either 3,3 is not supported by router or CA not supported, not sure.

JIO: i found BAND 3 and BAND40 in my area, BAND 3 has much better signal then BAND40, but my iphone always locks into BAND40 thus somewhat nil internet, luckily with the modem selection option i can select BAND 3 and some what internet is working. NO CA tried 3,3. 3,40 and 40,40 nothing Worked

Airtel: By default i see 4G+, i saw 3,40 but network signal is pathetic. 25% to nil hardly gets 1MPBS.

BSNL: tower visible through window next road, no 4G services yet (damn!)

My Question is weather Carrier has to support CA or This modem not picking up the band or if am missing something? 

for worth of the investment on this router, for me in order to exploit CA feature is to stick with Airtel, since by default its CA, i dont find any worth of manual selection since i couldn't achieve CA through it for jio or idea. if that the case i could have bought MR200 or MR 400 for half the price and in the forum i see beta relase which enables to select band.

I am planning to now buy and mount 12DBI LPDA hoping that i get the far away Airtel signal, On Amazon oxywave LPDA with 10 mts LMR 400 comes to 4k, since we need two it will come to 8k. but as suggested by few members here, HLF400 10mts with antennas in pair comes by around 2 to 3k. Am confused whether to go with oxwave with hefty price or to stick with chinese coaxial Cables for cheaper price?

@AkashDev 

Why don't you try something like this, which comes at < 5K cost?  

I myself have not tried this. I'm also in the same boat as you. This is one option I'm considering given the high cost of oxywave setup.

@AkashDev   check this video he has does this for less price. 

https://m.youtube.com/watch?v=Q6XRQCBg8wM

@TaZ30 I already ordered from the same seller waiting for that to be delivered. They Quoted - N F TO SMA M HLF400 10 MTR  - 490/PCS, 12 DBI LPDA  antenna - RS 550/PCS

shipping and taxes Extra. will try out the setup and post it here.Thanks for the video, i have now some idea

@AkashDev You have a choice to buy LPDA, which for sure will improve overall quality of signal and hence better speed. I am using LPDA for Airtel, with tower located about 500 meters away. ( I have one more tower just about 200 meters away, but no visibility due to my flat position in apartment).

I have 2xLPDA https://www.amazon.in/gp/product/B07ZJV67RN/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 

I bought LMR400 cable https://www.amazon.in/gp/product/B06XPC4S43/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I cut the cable, each of 5 meters. LPDA antenna in link is little legthy in size compared to other LPDA's in market. It is not YAGI, it is not 9/10 dBi. It is LPDA and it is 12 dBi. Product dispatched from Mumbai - with painfully bad packing. So if you live in and around Mumbai, yes you should buy. Else if you receive it with packet open, reject and buy again (may luck prevail here).

Used a PVC pipe, fixed on balcony rails and antenna mounted on it. 60-65 mbps download, 17-19 mbps upload is the speed I have now.

Importantly, I left TPLINK MR600 in balcony itself. Protected it from rain/sun with a postbox  https://www.amazon.in/gp/product/B07YFQ4K4Q/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

OK. Cost of Antenna INR 3198/- Cost of cable INR 1798, Cost of post box INR 650/-. Total cost INR 5646/-

Though fibre link is available in my apartment, I did not take fibre connection because of 2 reasons:

1. I live in a rented premise. I understood from service provider that I will have to shell out 3000/- towards internal wiring (Why will I do for a rented house?)

2. Frequent disconnections for users - more to do with rains, road digging etc., sometimes people with subscription wait for 7-10 days for service to resume.

If investment is worth, yes, please explore. May be, I also can be of some support to you.

@Abhi093 In the line of Sight, there is a building in between the tower. I am wondering if the antenna would pick up the signal. Need to check. thanks