If you try palace of the dead - solo - you start wasting a lot of those the higher you get.
At levels around 150-200 you might use above 100 of them per 10 level. That are 4-5 potsherds.

They are hard to farm because of the RNG loot of grey/bronze treasures which are often potions or phoenix downs and you want to avoid these at higher levels as well because of the chance that they are mimics/bombs.

With the sherds I get, I cant break even atm, I have to farm 1-50 or 50-100 to get at least 1 potsherd to buy another 20 sustain potions. It's annoying and that shouldn't be the reason which is holding me back to continue my other savegame...

1 gelmorran potsherd should give you like 50-100 sustain potions to compensate even more unnecessary grinding.