Initially I was on auto selection mode.
Due to my home poor cell signal reception, I was advised by Simba staff to manual select Simba network.
However, after more than a week, as I noticed no improvement to cell signal at home, I reverted back to auto selection mode.
No particular reasons for switching back to auto mode.
Now that someone mentioned that it bothers when across borders, then auto selection mode should be the correct mode.
Just in case when I am across the border, if I forget to set it back to auto, I may jump to wrong conclusions blaming Simba's data roaming.