I know but i guess i still prefer to switch tabs inside the browser and use the app switcher to change between apps.

It's normal for different people have different preference. What really bother me is that google remove the function rather than leaving an option for user to decide enable it or not. Actually , i am ok for setting merge tab and apps as an hidden option so normal user will not accidentally enable it, while at the same time other user can choose to enable it.

Not all people use this function in chrome, but there still need for this function. No browser has this function except the outdated google chrome v50. I understand that it will require a lot of work/changes to the code, but I believe this feature will attract more people to use opera for Android. Maybe you can add this feature in opera mini or news&search to test how many people really need it.

As you know, opera was sold. Is there any browser that have data compression? I have tried Google chrome but the data compression is not very significant when compared to opera. I know that there are many Chinese browser on Google play that claim they have data compression, but I'm fear that they are may collect password , bank info etc.
Any suggestions?

The spying of Microsoft, Google or even the USA government is COMPLETELY different from that of a Chinese company. What Chinese company will do is steal your passwords, bank account information etc(which is unlikely to be done by Google, Facebook or the USA government,they have no interest on that little amount of money in your bank account after all).Also a Chinese company may shut down Opera Inc after they acquired the data compression technology, or they may include some virus or malware in the new version of opera browser.