Does using 2 Sims slow down the phone ?No, and it's very hard to come by.
It was available in the following variants:
SM-G9550
SM-G955N
SM-G955FD
The first is Chinese as dragonheart786 has mentioned. English is available and you can get Google services but I wouldn't recommend it.
The second is Korean carrier version. Has English language available and with custom ROMs, you can remove the bloatware and Korean stuff.
Last is international variant and it's only being sold in the 6GB/128GB configuration in India and Brazil. So those will obviously be impossible to get. Has been launched in other countries too.
I am feeling significant difference with one sim
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