It is not a matter of trusting Vladimir at all (I do, but that is irrelevant). If you allow one unsigned driver you allow every unsigned driver.
And if you don't understand this then yes, I do think you are wrong.
Well, that is not exactly the case. You are disabling the enforcement of drivers to be signed. However, every single time you try to install an unsigned/untrusted driver you will be alerted by a big, red box where you can abort such installation, so I would say it is not that risky. You can always disable such enforcement and reject every single unknown driver installation except for TrackPad++, and nothing else will be installed. You are not consenting to installing every driver any program wants to install, you are only telling windows: "Do not automatically reject unsigned driver installations", so you will be prompted on every single unsigned driver. Once you have installed Trackpad++ you can start rejecting any other driver installation window that pops up, which is not common though, I have not had any software trying to install any driver on my Bootcamp partition.
I'd say that it is, as long as you trust Vladimir and act carefully after enabling test signing, as secure as having it disabled