What’s the benefits of having a silencer on a pistol?
Hearing protection. BTW they don't silence they suppress the loudness of the shot.
What’s the difference between a thread on or a built on silencer?
Integral suppressors make the overall package more compact, and in some ways can suppress the sound of the shot more due to the greater length of some integral suppressors. But suppressor wipes can wear out so for maintenance it's pretty obvious you're stuck with the whole package going in for wipe replacement.
But you're also stuck with the suppressor design that the integral approach gives you. Tech advances.
A thread on allows you to operate the firearm both ways. Plus easier to carry since the thread-on/QR suppressor = firearm makes for a longer package. And for wipe replacement you would just send the suppressor in.
What gun would you like to see with a silencer built on?
Personally, I think integral suppressor/firearm packages are very niche set-ups & more expensive. Having the firearm & suppressor separate is more versatile. If you have the tread-on or muzzle device QR versions you have many more options. I wouldn't buy an integral firearm/suppressor.
My .02