I have had a lot of success with Potters angels including pairs, but I have been keeping pygmy angels for a long time. They are hardy IF established. They are difficult to establish unless you are lucky enough to be able to observe one for several weeks at the LFS. You are almost never able to do so since someone always buys them without understanding their needs or problems. They are, however, suseptable to disease, parasites and/or stress more so than most fish. If you feel like your system is not very stable, you will have problems getting them established and keeping them established.
If you have other agressive fish in your system prior to introduction of the Potters, you will have problems.
Almost every single potters angel I have ever kept has nipped at sps coral polyps one time or another. They have never caused visible damage. This could be due to the number of corals in the system.