"OK button" can be used as a signature on all documents and this is a binding signing method.
This signature form is more secure than an old-fashioned signature made with a pen on a piece of paper. This is because a stamp is electronically incorporated into the signed PDF, in which various information about the signatory is stored.
Some of the stored information includes: IP address of the signatory, e-mail address or telephone number of the signatory, date and time of signature as well as an activity log which all become an integral part of the signed document.
A signature with an "OK button" is not as secure as a signature made with an eID, as it does not meet the applicable requirements given by the eIDAS regulations.
We recommend that you use a signature form that is supported by the eIDAS regulations
However, all options can be used as electronic signing, but there may be a difference between the level of security and the legal value.
Whether you sign with a touch signature or an eID, the signature will still be more secure and legally binding than a signature with a pen on a piece of paper.
You can read more about the different levels of online signatures here