He's not going to vivisect anyone. But killing the enemy is unavoidable in war. And they might as well take advantage to get the information they need.

Vader offered his hand, allowing Tech to deposit them, rather than him grabbing them. Some is simply knowing having a cybernetic hand grab your flesh and blood delicate body parts is often a threat, another is an attempt at not bowling into Tech's space. They didn't have the close relationship to allow it. But his shoulders still pull back just a little, he inhales oddly - sharp and quickly which is almost immediately halted then continued slower. And he speaks without exhaling. "Earcoms are not something I can use without them being wired into my helmet. My hearing was damaged on Mustafar and unable to be repaired." He loathes admitting that. To give any physical weakness out. "My outer ears were also severely burned resulting in nothing an earcom could hold onto." That bothers him less - he survived. Scars didn't matter.

Still, it was a huge extending of trust.