Our product currently is build on MX components, i'm planning to develop the future components in Spark components to take advantage of the skinning, not sure if we move the MX components over to the spark in the future. Does this cause any performance issues If I use both the MX and Spark together?
If you embed fonts you will probably want to handle all text the Spark way. You can use MXFTEText.css to do that.
You mean to say that the mx and spark components can co-exist with each other except the one which you mentioned above?
No, what I’m saying is that mx components default to using embedded fonts with embedAsCFF=false, and Spark is the opposite. If you are embedding fonts you would need to embed two copies of the font. However, if you use the CSS file I mentioned in your app, most of the mx components will switch to using fonts with embedAsCFF=true so you only need one copy. However, mx:TextInput and mx:TextArea will not, and they need to be replaced with s:TextInput and s:TextArea.