Ive had spigen glass screen protectors on my last two handsets and they are great. They are as smooth, if not smoother than the original screen and feel great to touch.
To apply (like any screen protector), what many people recommend;once fully cleaning the screen, leaving the protective film applied, position the SP on the phone exactly where it should go, and use masking tape down one edge, securing it to the side of the phone, so its like a hinge. test 'opening' it a few times to make sure it then sits as it should.
Give the screen a final screen and then take off the film on the screen side. Flip the cover onto the screen and smooth out any bubbles. Take off the tape and last protective film.
Ive read that some people will only apply them in the bathroom, after they have had a shower. This is because the dampness in the air helps stops as much dust in the air.