Private companies can benefit from retaining a professional transfer agent.  I had written about this for our company web page - see the link below.   If there is a lot of growth in the number of shareholders on your register, if you are a dividend paying company, if the quality of the shareholder recordkeeping is poor ( missing addresses, inconsistent structure of the data being kept, incomplete share registrations) and if data security concerns exist - you should retain one.  See the link below for more information.  I would be happy to discuss - send me a note.

https://www.computershare.com/us/news-insights/insights/industry-regulatory/transfer-agents-not-just-for-public-companies