Using a flat pen does no harm to the ipad.
The core of Apple pencil is the pencil bar, the principle is mainly electromagnetic induction, which is different from the flat capacitor pen that simulates fingers by current.
Paper tape nib sleeve or tempered film these substances do not have the function of electromagnetic shielding, but also in the induction distance, so it is not affected.
Many third party nib construction is the same as the original, there are metal contacts, thread fit, there is no problem.
In general, the use of flat pen for IPad tablet will not damage the iPad product. This third-party pen may not be as good as the original pen when using the connection, but it can meet the daily needs under normal use