The plastic ones work the same, but they have a transparent cap and rubber seal design, so just have to make sure its fixed properly to avoid leaks.
The single piece glass ones don't have potential issues with rubber seals so they could be considered having less chances of leaks, though if they drop inside the tank, the indicator solution will still spill out, so have to secure them properly with the suction cups.
Another alternative is to look at the hang on glass drop checkers, they hook on the tank glass with the indicator part outside of the tank, these ones will eliminate most issues with leaks or spillage.
Looks like this:
Photo from Google Images.
Can order them from online sites or bought at most LFS. I use them in all my tanks nowadays.
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