Pros
Really friendly to telecommuters; I have worked remotely for a lot of shops over the last ~10 years and Tenable does this right. No nonsense, no preferential treatment. My manager at least was one of the most laid-back people I've met, professionally or otherwise. Despite disagreeing on a lot of things, coworkers were easy to get along with. If you're looking for easy work and are a halfway competent programmer, you'll find it here. I, however, want to be challenged (see below). For a less experienced developer looking for a place to grow in the beginning of their career, Tenable would be an okay choice to learn the basics. It's an extremely forgiving environment where (at least on the team I was on) mistakes won't cause business-disrupting catastrophes. This is great for newer developers, but I needed much more culpability in my work (again, see below).
Cons
I wasn't challenged, at all. Most of the job was maintaining existing code and there weren't any hard problems, just "fix this" and "incrementally improve that" or "copypaste this and slightly modify it to suit this new thing". It was tedious, unrewarding busy-work that doesn't make me excited to get up in the morning. There were no real challenges in sight, just keeping up with the endless tide of small changes and fixes. I couldn't see myself doing that forever; it was a shameful waste of my abilities. There were no real risks, either. Nothing I did had any risk to it; either the code didn't work and harmlessly failed or it did what it needed to do and the world marched quietly, uneventfully, on. Sure, I was helping make the internet incrementally more secure, but not in any real, measurable, lasting sense. It was like I was adding bricks on top of an already-built dam. I was improving the situation, but drastically less than the people who came before and built the framework I improved every day. I identified with the mission (just not in the way the marketing department phrased it), but without a sense of being challenged I felt like I wasn't really improving myself, like I was standing still in the most rapidly moving field on the planet. Technology-wise it's a very corporate environment, very unfriendly to open source. This was probably the basis for everything else that put me off the company. Note that this was a con from *my* point of view, and that others may prefer it. I know my coworkers certainly did.