There are lots of companies that succesfully use CRM Systems. In my opinion, before investing money or time in a CRM system, you should try to understand what a client relationship management system does and how it can improve the way your company operates. A CRM is used to basically help a business turn potential or future customers into leads, sales and money.
It sounds good but before investing try to find that gaps in your company that a CRM system could fill before finding what CRM could help you. To answer your question, CRM systems are indeed succesful and there are both big and SME companies that use them in a profitable way.