There is a difference. Actually 4xMFAA has the performance cost of 2xMSAA, but with anti-aliasing equivalent to that of 4xMSAA. MFAA/Multi-Frame Samples Anti Aliasing offers MSAA quality, at a way lesser impact on overall performance.
MFAA is close to MSAA quality wise, and effects it, when this mode is enabled. It doesn't blur the image that much. The end result which you can get is that MFAA, can deliver Image quality same as that of 4x MSAA at roughly the performance cost of 2x MSAA, or 8x MSAA quality at roughly the cost of 4x MSAA.
MFAA/Multi-Frame Samples Anti Aliasing offers MSAA quality, at a way lesser impact on overall performance. You can enable and force MFAA via the NVCP. Like e.g., 4xMFAA has the performance cost of 2xMSAA, but with anti-aliasing/AA equivalent to that of 4xMSAA. So 4xMFAA would, ideally, take a 2x MSAA performance hit but offer 4xMSAA quality, if not a little higher.
The end result which you can get is that MFAA, can deliver Image quality same as that of 4x MSAA at roughly the performance cost of 2x MSAA, or 8x MSAA quality at roughly the cost of 4x MSAA. IMO, MFAA is close to MSAA quality wise. It doesn't blur the image much, unlike other AA modes (btw, it's 4xMFAA, not 2xMFAA).
Like e.g, for the game GTA 5, If you've opted for Multi-Sample Anti-Aliasing (MSAA) option in the Video Game settings (e.g. 2x, 4x etc.), then you can enable/force the 'Multi-Frame Sampled Anti-Aliasing' (MFAA) option via the NVIDIA Control Panel (global settings), for better performance.