Can anyone explain the functional differences between this two handguns ?

From what I understand, the TP9SA is a Gen1 TP9 with single action only (and retains the decocker...). The TP9v2 has a redesigned grip and frame and reverts back to the DA/SA set-up of the Gen1 TP9.

https://youtu.be/VTWBNX_GChE

SA is single action with a decocker that renders the gun dead the V2 is a DA/SA and the decocker puts it in double action. they are coming out with a new model called the SF which is like the glock no decocker single action I have a feeling that they are going to fly off the shelf.

maybe, if they shrink it down to G19 size too

Am I missing something.  Isn't this V2 trigger just the same at the originall Walther P99 anti-stress trigger they have had since the 90's and the first TP9 is just the copy of the P99/SW99 quick action trigger that nobody liked??  David

I don't understand a De-cocker on a single action only pistol....  What if you are carrying cocked, with one in the chamber,  and you bump the De-cocker without knowing,  then you need to draw your weapon....  You have to rack the slide when you find out the gun won't fire....

I have the V2

Agreed. Make it Glock 19 size, or a hair smaller.

too late goose, they F'd it up again

I would say it's because you're not thinking like a Turk.  They designed these pistols for military and LEO usage but in Turkey, sidearms are carried in condition 3, loaded magazine, empty chamber needing the shooter to rack a round into the chamber before firing.  Now for Johnny Turk, he draws the pistol, racks the slide and shots are fired.  Now rather than try to eject a live round and insert it back into a magazine after a defense shooting is done, I depress the decocking plate essentially leaving my pistol back again into a quasi condition 3 before I reholster it.  Now if the need to use it again comes up, he draws the weapon, racks the slide like he always does with the same muscle memory.  Well, at least knowing how the Turks operate, that's my best guess as to why the decocking plate exists on the TP9SA but it's a plausible guess in any case.  
Now that all being said, it doesn't appear to be a complex or expensive procedure to deactivate the decocking plate with a wire coat hanger.