I'll preface my post with the fact that I'm a simple enthusiast. I just try to have fun with the hobby...
I bought a 150-600 G2, and it was my first "decent" lens. Have since bought a 24-70 2.8 and 70-200 2.8 Tamron as well. Very happy with the 24-70. Jury is still out on the 70-200, but given I occasionally get some incredible shots with it...thinking it is probably me, not the lens. Or, don't have the body set up quite right for the situation.
Has seen some comment on the extenders. I can't imagine trying to use on on the 150-600. However, I'm seriously considering one to use with the 70-200. I really like the size of the 70-200, and that it's internal focus. And with it being relatively fast, hoping it will be a good all around package to work with.
Would also have to agree with comments on the 150-600 being a good "bright light" lens. Have tried to get a few birds shot with it, but for me, that's always late in the day, and it does struggle in lower light.
Went out this morning and took a few shots as examples of what I'm getting with it. These were taken mid-morning, high humidity in tropical environment. So fair bit of haze, in general. Hope they help you get an idea of what the lens is capable of with a fellow amatuer...
All of these are uncropped, with only minimal "auto" correction to be able to export from RAW to jpg. All as wide open as the lens would run at the focal length. All auto white balance, spot metering and, for the most, single point autofocus, and with the exception of the first two that were locked at ISO 100, set for auto ISO at 6400 max. Shutter speed (I think) mostly at 1/1000, but I may have "intuitively" rolled the shutter speed if the bar in the viewfinder tapped out the ISO. Also set for +2/3 exposure compensation. Canon 6D mkII. Most on a monopod with a gimble. VC on, set at VC mode 1.
First one was taken with the 24-70, 24mm, f2.8 to give an idea of the environment. Second one is at 600mm on the cupola in the center of the first shot way in the back. Probably about 400 yds-500 yds away. You'll need to download and zoom in to get an idea of the IQ.
I don't get as much of an opportunity to use it as I would like, but have been reasonably happy with it. Hope this helps.
You mileage may vary...