The developer tools on Chrome give you a pretty good indication as to how the site might render, however they are all being rendered using the Blink rendering engine so you won't get the nuances of difference browsers on the devices (seeing as you mentioned opera mobile emulator).
There are two factors when you're looking at this.
One is how the site renders upon a mobile. This is based upon device/viewport width, connection speed, hardware acceleration, additional input types (gyroscope, accelerometer, touch etc). This is difficult to test on an emulator.
The other is how the site renders upon a mobile browser. This is based on viewport width, connection speed, user agent strings etc. These things can be faked using the Google Development tools mobile view and tweaking the device type, user agent and connection speeds (although mobile latency won't be a factor here).
The harsh truth is yes, for best results you need to try your site on a whole bunch of devices. You can find Open Device labs that help out with this stuff, [
opendevicelab.com...] and you can try [
browsersync.io...] if you have the devices yourself.
