I'm no professional so take what I say with a grain of salt, but I imagine soft glass is just lighter/ more fragile
I'm not sure exactly, except the glass isn't pyrex or anything decent, its most likely somewhat porous. They're almost all if not all grommet bongs. So they're most likely just mass produced "sweat-shop to head shop", and that being said, sizes seem to often be wrong, making everything that much harder due to lack of parts for anything not GonG these days. That's mainly speculation, so take it with a grain of salt.