While I recommend Adonit stylii ( www.adonit.net ) as the ONLY third party, smart Bluetooth alternative, even these are not as reliable, flexible, respionsive and as accurate as Apple's Pencil, mainly because third party stylus developers have NO access to Apple's own Pencil technology and have to attempt to guess or reverse engineer a version of a stylus that works “approximately” in the same manner as Apple's Pencil with different accuracy and response differences.
Such stylii need to have specific apps that support and are compatible with third party smart stylii as the third party stylii, usually, needs to be Bluetooth paired within the compatible app and not just paired, globally, for the entire device.
Adonit smart stylii all feature palm rejection that can be sometimes not 100% reliable and many of their stylus offerings have screen pressure sensitivity for thin to thick and light to dark writing/drawing marks on screen.
Not all Apple Pencil compatible apps are compatible with other third party smart Bluetooth stylii amd those that are, will be far fewer than apps compatible with an Apple Pencil.
Third party stylii, like from Adonit and Logitech, will be chaeper,,but only because of lesser performance and/or missing or lesser accurate features to their stylii.
Third party stylii can still be considered viable alternatives to the more expensive Apple Pencil, but you need to research the smart, Bluetooth stylii to see what apps such a third party stylus is compatible with.
It all really comes down to price VS performance of a smart stylus.
Apple teamed up with Logitech and shared their Apple Pencil technology with Logitech to make the Logitech Crayon.
https://www.logitech.com/en-us/products/ipad-accessories/crayon-ipad-digital-pencil.914-000051.html
This stylus is cheaper and functions almost the same as an Apple Pencil.
It is as accurate and as responsive as an Apple Pencil. The Crayon has Apple Pencil tilt support and palm/side of hand rejection.
The only downfall/drawback with the Logitech Crayon is that it has NO screen pressure sensitifity for thin to thick or light to dark writing/drawing marks onscreen, which may be a missing and desirable feature ONLY found in the Apple Pencil,,itself, and other third party smart stylii.
Best of Luck to You!
