Do you mean slide out on their own? If so the answer is no, not all plugs slide out. I would say that the Sassi is more of a probe, much like a dildo for your ass.
A good plug should slip in easily and stay put until you take it out. Look for something with a marrow "Neck" below the bulge, this helps to keep it in.
Here is a good example for you.
As you can see the body of the plug narrows down after the bulge, this also helps with long term wear as you anus is not stretched out the hole time.