Useless stuff Tim, any weight and it will pull it and the pole off the plaster. When you drilled could you feel the RSJ or a void ? There are ways to fix into RSJ .Not something I swear at really Allen. It’s just sticking plastic together and throwing paint at it.
If you want swearing you should have heard me trying to put up curtain poles a couple of days ago….RSJ lintel and no wood blocks to screw to equals total nightmare. Looks like “no more nails” to fit wooden rails before I can get the poles up…..