Metabones Mk 3 vs Mk 5?

Hello,

So I have got a Metabones EF to E adapter from eBay personal seller today. The adapter is the same as shown in the image, but looks like he misidentified it as a Mk V, while actually been a Mk III. I have checked with the Metabones app, and it indeed lacked the ability to toggle between "green mode" and "advanced mode" within the app as supported by Mk IV and Mk V adapters.

I am preparing to negotiate with the seller about what to do. The seller does accept returns, but since the adapter itself is lightly used, I do consider trying to get a partial refund and keep this adapter (which would then be a very good deal). Therefore I would like to know the following:
- I have read that the AF performance (when using the same firmware) are basically the same from Mk 3 to Mk 5, is that correct? From what I have read, the Mk 4 and Mk 5 are mostly physical updates that benefit perspective-control lens users, which I am not one of them.
- Does Metabones have any plans to discontinue firmware updates for older adapters? I know the Mk 3 has been officially discontinued, but it still receives the latest firmware, so want to double-check if there are any plans on discontinuing support for the Mk 3 adapter.