One thing to remember with glass and other rigid materials: they have no give whatsoever, so they feel bigger than soft toys of the same diameter. It's advisable to go down a little in size compared to what you're used to when you first try glass. Also, because it's firm and heavy, you have to be gentle when you use it. Internal bruises aren't desirable.
But if you keep these things in mind, glass can be quite nice. And yes, lube is your friend, though glass is pretty smooth on its own and doesn't drag much. Too much lube can make it super-slippery.
After reading and educating myself on jelly, I'm no longer a fan. I'll be sticking with silicone toys for those times when I want some give to my toys and I'm taking advantage of the face book offer for my first glass toy.
If you like the softness and flexibility of jelly, go with silicone for something safe but still pliable. Just look for toys that don't have a hard core. If you want to try something firm, silicone skin on a hard core or glass is awesome, super safe, long lasting and a favorite for many. Jelly has a lot of drawbacks and safety concerns. I stay far away from jelly and other porous materials.