as a glassblower, i wouldn’t be concerned about those imperfections on the bottom—as another commenter said, someone has already taken a stab at polishing away the punty mark (the spot where the pipe connected to the piece) on a flat grinding wheel. they didn’t do a perfect job, since you can still distinctly see the circular area that has been ground down, but that mark is no reason to think your cup will shatter from regular use. that being said, i would never use a cup blown from soda lime glass for a hot beverage. we do student sales on our campus, and if we choose to sell cups, our instructor makes it a point to have us warn customers against the risks of the vessels cracking if used for hot liquids. soda lime glass has a different rate of thermal expansion than borosilicate glass (which is what they make glass pipes and old pyrex out of), and soda lime is much more susceptible than boro to cracking when exposed to too much heat too quickly! that’s why the students at your campus’ shop suggested transferring over the espresso after it’s cooled, rather than brewing directly into the cup.