Use of a screen protector is largely personal choice - but there are considerations.
iPad screens are robust, but the anti-reflection treatment and oleophobic coating can be easily damaged by tiny grit/dust particles that are unavoidable in many environments. The oleophobic coating is a chemical sacrificial layer that will wear-out over time.
Your iPad screen is the single most expensive component of your iPad - whereas a screen protector is sacrificial layer that, if damaged, is easy and relatively cheap to replace.
Zagg and OtterBox are amongst the better manufacturers of tempered glass screen protectors - with good reputation. Always choose a screen protector from a well known brand - choosing a screen protector that is specifically designed for your iPad model.
Some users comment that a glass screen protector makes the screen very slippery when using the Apple Pencil. The alternative is a matt/textured film screen protector - but these have two principal disadvantages.
1) The textured film reduces clarity and contrast
2) Accelerated wear of the Pencil tip, necessitating frequent tip replacement.
Good quality tempered glass screen protectors from reputable manufacturers, that are designed for your iPad, will have absolutely no impact upon sensitivity of the screen or usability of an Apple Pencil. By contrast, cheap “generic” screen protectors of any type, whether glass or film, can cause problems. The good options often include a money back guarantee.
Of available options, Zagg arguably have the best reputation; you are very unlikely to find reported issues or complaint with their screen protector products.
Also consider that physical screen protectors can be removed without affecting your iPad warranty. Liquid screen protector products offer no physical damage protection, are irreversible, and may void your Apple warranty.
