Me and some friends who own an AMD video card checked out Battlefield 4 with the AMD mantle API. Our first impression is that it is too earlier to play with it. We used it over 3 hours and we all said that it will boost the game performance and it is really noticeable and measurable. However, there is a problem of regular heavy frame drops and we all wondered if this is a problem with Battlefield 4 or the latest AMD beta video drivers.
What ever the reason is, we decided to go back to DirectX today but that does not mean that we won´t check out Mantle again. As said… I think it is just an issue that must be fixed or the driver or code and performance must be optimized first. Well, we talk about beta drivers and AMD mentioned on their Facebook page that they do work on optimization. They mentioned that they still need to optimize the performance with the 280X, 270X, HD 7000 and HD 8000 with the drivers. Anyway when I forget the frame drops, then I would say Mantle has potential.
The game was much more fluid on my 270X than if I would use DirectX. But the frame drops every five seconds or so, did annoy me pretty much. This must be addressed by AMD first. Friends and me were all the same opinion that you otherwise would not be able to enjoy the game performance due to the frame drops.
Diary of Dennis 
in my case mantle works slower than dx11, unexpected by me. i have a r9 270x with a FX 8320 @ 4.2ghz
Ok but as it is still beta, we might wait to see how it works in the future. I think it is nothing than a first impression at the moment. I hope they will optimize the drivers so that we all are happy with it. Until then, I still use DirectX as well.
r9-270x here using beta 14.3 still getting bad frame drops and stutters every 5-10 seconds. waiting on 270x optimized drivers from amd still.
Yes, I have the same experience. Didn´t improve for my 270x too. Hope they sort it out soon. At the moment I still use DirectX.