Orangehrm Not best for the Customization!
All is Okay because it is a open source and they have developed orange hrm with "Symfony" framework.
But if you go with the Customization for your company or a client company, to change the orange hrm logo or orangehrm links then you will feel that it is not easy one.
And i am sure that there is no proper documentation for orangehrm. So all you have to do, you need to refer symfony framework documentation only.
Please suggest if i wrong on this.