Unfortunately, the description of this product was not full or clear.
Buying the item like this in second decade of the century suggested that BOTH SIM cards can be used for calls / SMS reception simultaneously.
This is wrong! All this adapter does is prevents a user from opening SIM slot and changing the cards. A bit too expensive price for such feature.
Moreover, as another unhappy user already wrote, the SIM cards must be on the same network. I believe, this was a reason why my second SIM from another country (on roaming) was not found at all. And the first SIM kept dumping APN settings. In addition, the network tracking became unstable. When I changed back to original single SIM, all settings and network quality had restored.
From my point of view, this adapter is waste of money, and is, for its single feature, too expensive!
I wish I could return it, but I destroyed the package and thrown out the shipping docs.