A professional management company is usually a good idea if the dollars work out right and if the management company is reputable. Professional management companies generally have the contacts and expertise to quickly find tenants and manage your property to maintain its value. The company will be much more familiar with legal requirements than you, have all the right forms, and have the software to do things more efficiently. They are less likely to become personally involved with a tenant, and therefore better able to be strict about timely rent payment and other requirements. A good management company will keep your rents at market rates, and advise you when you should raise the rent.
The problem you have as a flipper is that you are probably a project-driven person. You like to throw yourself into something, get it done, and go on to something else. You are usually not the type of person who likes to deal with the routine and never-ending chores necessary to properly manage a rental property. As a result, most of the time these things just do not get done. It is better that you should recognize this about yourself, and hire someone else to handle the management.