Why is glass a widely recommended option for the print bed? Glass is really bad at transferring heat. Therefore using it with heated bed seems to be a strange solution since it will not be transferring heat from bed to the print.
However every article I see says it is actually good solution for printing.
The reason I am concerned is that I have pretty large bed (500x500 mm) which is pretty hard to keep flat. And in this case glass would be a good top surface that will keep bed rather flat. But same time I am concerned that it will kill the benefit of heated bed (PCB style) and will require higher bed temperature to get glass surface to equal temperature.
I suggest to look at a similar question, but just the glass question here:

Glass is a very smooth surface
Glass shrinks when cooling to a degree it pops the print free on itself
Glass is virtually impossible to scratch with metal scrapers
Glass stays fairly flat under heating
Refurbishing of the bed isn't needed but for applying your adhesion solution (Woodglue, Gluestick, Hairspray, 3DLac, ABS-Slurry... pretty much ANY glue can work
Glass is one of the few surfaces upon which almost all materials can be printed without risking ruining your print surface on removal

PETG is one of the few that demands some sort of extra adhesion material with glass, most others don't need anything.
POM and some other materials love to rip PEI apart
I had a huge PLA-print stick so well to a BuildTak that I had to cut the sheet off the bed to get it off



The problems are fairly evident on the other hand:

Glass is brittle and shatters on impact or thermal stress.
Good glass can become rather expensive if you want a super flat sheet in non-standard sizing and a specific type.
Large glass sheets need a very even heater to prevent thermal stress.

Borosilicate?
Borosilicate glass (&quot;labware&quot; glass) is more resistant to thermal stress but also does not pop free from the print the same way as normal glass does. It is also more sturdy but MUCH more expensive. It also comes with its own problems:
Some people have experienced spalling in combination with PETG, as it created a perfect airtight seal, making an adhesive as a separation layer mandatory. This behavior was also reported for normal glass, which is why an adhesive material is strongly suggested for this material.