Our handbook set out an introductory period of 90 days. We say we are“at-will” employers. Is this good?

Yes, but you must ensure that your at-will policy states that you may terminated under your policy at any time during the employment relationship, including during and after the introductory period. Furthermore, it isalways advisable to have good, written documentation as to the reason for the termination, in case the former employee alleges harassment, discrimination or retaliation subsequent to the termination.