Pipe in India most likely conforms to (BSP): ISO-7-1 British Standard Pipe Taper (BSPT)
INDIAN STANDARDS : Bureau of Indian Standards (BIS) have so far not developed an Indian Standard for the design of Piping Systems. Hence, ANSI Standards ASME 31.1 and 31.3 are widely used for the design. These standards also accept materials covered in other standards. Unlike American Standards, Indian Standards cover dimensions and material specifications under the same standard number. There are no groupings based on branch of engineering. Some of the most commonly referred Indian Standards by Piping Engineers are :
[truncated, see link; e.g., IS 554 : Dimensions of Pipe Threads]
There are certain other international standards, which are also referred in Piping Industry. These are DIN standards of Germany and JIS standards of Japan. DIN standards are more popular and equivalent. –CODES and STANDARDS, www.svlele.com
IS 554 : 1999
IS0 7-11 : 1994
"This Indian Standard (Fourth Revision) which is identical with IS0 7-l : 1994 [...]" –law.resource.org (ISO-7-1 British Standard Pipe Taper)
Which means you'll need an adapter that gets you from NTP to BSPT
Then again, according to this table (BSP vs NPT), 1/2" and 3/4" pipe both have 14 threads per inch, and the pitch of the threads are only off by five degrees, so I think a copious amount of PTFE tape would make a shower head work just fine. But don't quote me on that; I've never encountered BSP in the field and had to make it work with NPT fittings.
It has been mentioned that, "That model, it super sucks. The flow is extremely low." Might I suggest that you install a (valved) wye fitting and have both shower heads. Use the new one only for doing your hair so as to not prematurely clog the filter.
Debris. Mineral buildup, sand, etc.... You loosened it up, when the water came back on it pushed it into your valves and aerators. Pull the aerators off and clean them out. Of it improves, no need to pull the valves out. Of better, but not the way it was before, turn water off statue faucet and pull the valves out and clean them. I just did the same thing 2 days ago and have 1 more faucet to clean the valves in.
Best Answer
Yes a very clear advantage. Use the first tank to take the water from street temperature to say around 90*. Use the second tank to take it form 90* to the 120* or whatever temp you want at the tap. You will have considerable more capacity. There are a number of additional advantages as well. Happy Heating. P.