.localhost was created in 1999.

It has no advantages or disadvantages. localhost is a domain name that represents your computers local IP address.

a-localhost.net is an internet location that provides 'shortcut syntax' (intuitive, easy to remember) urls providing 'direct' access to internet connected resources and services intended for use by 'a localhost'. 'A localhost' is defined as 'the local computer (or device)' (ie. the computer/device you are currently using is considered the 'localhost)'.

To test PHP on your computer you can use a localhost. I use XAMPP for my localhost and it hasn't failed me yet.

localhost