When it comes to credit card processing SAM4s is flexible with who you can process with and what pin pad you can use. SAM4s is credit card processor agnostic and you can select your own processor or operate without integrating of course. It is best practice to integrate because an integrated system is much faster and few less prone to costly mistakes or fraud. Currently there are numerous pin pads compatible with SAM4s registers.
Pin Pads are a must for electronic payments of course to limit your exposure to EMV chargebacks and credit card fraud. Since the EMV liability shift happened quite a few years ago now I don't think we need to explain why you need to use a pin pad instead of a magnetic card swipe. If you are unsure about EMV liability please ask your merchant services and if your merchant provider does not know the answers find yourself a different processor.
Here is a selection of tested Pin Pads for most SAM4s system. Of course there are other factors like the processor and functions you require. As an example do you need to accept Pin Based Debit or perhaps accept EBT? This features usually depend on who you process with.