Running romex in 20" attic space using pipe hangers
As mentioned in a comment, those are not listed to be used for electrical cables. If you are just running one cable in one run, just use regular NM cable staples like these:



If you are running multiple cables and would like to save some time, you can use "stackers" like these:



If you added another 2x4 to the side of the members that run perpendicular to your joists, you could also just use that as a raceway and run your cables in there.

Edit: To answer the second part of your question, it will be fine for the cables to be in the blow-in insulation. If you think you will be doing lots of work up there and changing things around later, you might to have the cable up higher so you can find them easier later. But that is personal preference.

You may also want to look at this question, it goes over the requirements for additional protection if the cables are in an accessible attic (vs one without access).