Can i use doesn’t have mobile data? http://caniuse.com/#feat=flexbox

If you want good compatibility, just use autoprefixer and it will automatically add the prefix of the old syntax for you
or use a framework like bourbon to add the prefix

In addition, some features are not supported by the old syntax, but can i use are written.

.flex() {
    display: -webkit-box; 
    display: -moz-box; 
    display:-webkit-flex;
    display: -ms-flexbox;
    display:flex;
}

It can be compatible with ie10 and above. There are basically no problems with other web browsers. It is hard to say about the mobile version. There are no problems with ios. However, there are too many third-party browsers for Android, such as UC, and the kernels are all very old versions.