It's a tactics to force consumers to buy higher storage solutions just like Apple do so that they can earn huge profits from extra few GB storage space which in SD card cost few hundred rupees but they are changing few thousand for that.
I'm using 2 sims +sd card on this phone. Its actually very easy, but requires concentration and precision.
Use videos from youtube for reference.
My advice:
1. Before removing plastic part from sim card, mark one of the sides to know the direction you need to insert.
2. Don't try to remove directly. Make the plastic a bit warm(not much), before removing with a nail cutter.
3. Use a light gum along the sides of sim to paste the sim on the sd card. Don't insert tray without pasting, as it may get stuck.