This pen DOES have pressure sensitivity. Those who said it doesn't didn't follow directions. (See my first picture for proof)
First off, this pen is only able to use its shortcut button and pressure in supported apps. If the app isn't supported, you're no better off than using a normal capacitive "dumb" stylus.
To see which apps are supported and for which platform, go to SonarPen's website. You can also see what apps are currently in development for upcoming support in the future. For example, Medibang only supports SonarPen on iOS! Andoid support is still under development as of the date of this review. If you're on Android, in my opinion your best bet is Ibis Paint X. The pen pressure and shortcut button works wonderfully in that app. Make sure to go into your settings in the app to enable SonarPen support! You can configure your pressure curve and button mapping there.
Another thing to note about using this pen on Android! The palm rejection will not work, or at least it's very unlikely. It's a limitation of Android screen hardware. I just use a glove for palm rejection. I can't speak on how effective the palm rejection is on Apple devices but it is supposed to work much better.
Something to note about using this pen on iPhone, I haven't personally tried it but multiple iPhone users have confirmed this pen works through the lightning port to aux adapter.
If you loose pressure sensitivity part way through a painting, in my case I realized it was because Android was trying to save my ears and prevent me from using full volume with the aux plugged in. (You need to have media on full volume for this pen to work at its best!!) If you download an app called Volume Lock and set it to keep media volume at 100% that'll do the trick!
As you can see this pen is on the larger side. I've got it next to a Meko stylus and a soda can for scale. I do wish it came with a cap to protect the flexible disc nib. The disc is your friend by the way. If you have a regular capacitive screen a skinny nib stylus will not work nearly as well for you because they're designed to sense finger tips.
Another gripe is the cord unfortunately registers as a touch input so it'll mess up your drawing if you're not careful and you let it slide around the screen. I just rotate my screen orientation to ensure the aux jack is on the same side as my drawing hand and then the cord is out of the way and not an issue.
I would say this pen is a great choice if you have a device that doesn't support S pen or Apple Pencil so you can still get the smart pen experience! (Not as nice of course, but for a fraction of the price)