Before getting turned on to Gardz I would use 123. The advantage of Gardz is that it can be hung over really quickly- as explained by Pro Wall about the paste not rewetting or softening the primer.
The downside is that it has no pigment, so harder to see any imperfections that need to be dealt with .
I sometimes add them together to get a bit of both worlds, better if you can wait a bit before hanging over, just in case.
Both will adhere to the plaster just fine.