Hi, is there any way to use feathers sdk with FDT, try different ones without result
I have not tested with FDT. The Feathers SDK is designed to look similar to a Flex SDK, so most IDEs should treat it as a valid SDK. However, like Flash Builder or IntelliJ IDEA, there may be some issues because these IDEs aren't designed specifically for Feathers. You may be able to tweak some project settings to make things work better, but I couldn't tell you what exactly is required.
btw way i encountered the AIR 25 sdk error (mentionned in another topic) while installing Feathers SDK
This is a known issue for now. As a workaround, you can either use an older AIR SDK version or you can manually install the Feathers SDK with Ant.
AIR SDK 25 is significantly larger in file size than previous AIR SDKs. The Feathers SDK Manager and Flex SDK Installer both need to load the entire SDK into memory for various purposes, and this can sometimes require more memory than a 32-bit process can allocate.
Adobe is working on a 64-bit version of AIR for Windows. It's in beta right now, and when they release the final version, I will release an updated version of the Feathers SDK Manager that is 64-bit and can handle the larger AIR SDK 25.
1) is there any performance difference betwen Feathers AS3 vs Feathers MXML
2) is it possible to use Starling display elements like Canvas, RenderTexture with the MXML syntax like <s:RenderTexture> or <s:Canvas>
No. Only Feathers components are available in MXML. However, even when a Feathers component is created in MXML, you can still add Starling display objects as children in ActionScript.