The stability has been excellent, almost perfect. A couple of caveats: 

If you have to do a lot of trending dashboards, Security Center will come to a screeching halt. We had to be methodical about when we schedule our trending dashboards. 

Also, the way you design or create your repositories in Security Center needs to be well thought out, because there's a direct correlation between the size of the repository and how much memory you have on that given server. In other words, you can't create one repository and put 150,000 assets of data in it. It simply won't work. We found that out the hard way. We didn't know that going into it.

We redesigned our repositories. We have a repository just for our agents, we have a repository for each of our subsidiaries, we have a repository for our compliance scanning, etc. We have something like 25 or 28 repositories.

But the stability is, for the most part, rock solid.

It's been pretty stable ever since we implemented it. It is working fine.

So far we haven't seen any stability issues.

Tenable is a very stable solution with no downtime. It is smooth, no problems.