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. There are other cheaper Screen Protectors from other manufacturers, of varying quality - many of which are available from Amazon.
As with most products, with Screen Protectors you get what you pay for; cheap doesn’t necessarily equate to a good option. Some screen protectors don’t work particularly well with iPad - some reducing screen sensitivity, in particular with an Apple Pencil.
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.
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.