I own a TP9SA and TP9V2. The main difference between the V2 and SA externally is the SA barrel is .47" longer, 4.47 vs. 4.0 on the V2. The V2 is DA/SA, where the SA is single action only. I have a coworker with a VP-9, and we've done back to back comparisons, putting a magazine through each and have agreed, the single action on both Caniks is perhaps a little grittier than the VP9, but breaks just as cleanly, and actually has a nicer reset. The DA on the V2 is quite tame compared to a hammer gun like my P01 or P09.
The V2 addresses the "issues" youtube reviewers have with the TP9SA and it's decocker: you can decock with a round in the chamber, draw and fire without needing to manipulate the slide. But, as Brian Ahern noted in another forum here, it's extremely unlikely that you're going to decock the TP9SA by bumping it on your holster, a table, etc. The decock button requires a solid push to actuate, which pretty much limits it to an intentional act by the user. IMO, it's not any less safe than carrying a Glock or M&P with a round in the chamber. Don't want to have to cycle the slide in a hurry, don't decock it, simple as that.