Pros
Let me preface this by saying that I worked at HubSpot before and after a large disruptive shift in how the company perceived its employee pool. The developer pool at HubSpot is still quite talented and there are some very good developers there, or what's left of them at least. On certain teams you can work with and learn from some great developers. Company does actually let you take time off through its honor system time-off policy.
Cons
The last several months I worked at HubSpot could be gently called a witch hunt, as leadership decided they wanted a disruption in the company to reshape the development team into a specific mold - that mold being one of decisions driven more by impulse and the mantra of "just do it" rather than "just do it (conscientiously)." People who didn't buy into the new world order left, and others were unceremoniously terminated. Team cohesion became very disjointed, it was very much like seeing two separate teams - those that wanted more conscientious change, and those that told the other side to shut up and do as they say. I'd say if you're a certain type of developer - one who claims to abhor process and wants to produce prolific amounts of code which will then probably be rewritten multiple times in short order, and want your developer philosophies heavily mixed with a heavy side of uncertainty and frenetic chaos, you will fit well into the new world. The benefits, for those that care, are very much what you'd expect from a start up. The vacation policy is the selling point, and you certainly won't starve on your pay, but the promise of IPO dollars is part of the package. There is no 401k match.