Pros
The team is friendly, dedicated, hardworking, and does things the right way, instead of taking shortcuts. The two founders both have expertise in law *and* software development (expect to learn a lot about either/or, depending on your role). This is critical when running a legal technology company, because a typical startup "move fast and break things" approach can cause problems easily, while looking at things only from a legal perspective will leave you with software no one wants to use. The working hours are generally flexible (though often long, as with many startups) and "fire drill" type situations are very rare.
Cons
The work demands a level of attention to detail (and focus) that is rare outside of niche specialties (like public company work at a top law firm). That doesn't sound that bad, but it can be a big con depending on your personality and work style. Additionally, there are a lot of public misperceptions about what the company is actually doing/building/innovating. Doing anything disruptive and successful in the legal technology space generally requires a very long time, by nature of the industry - the company is definitely running a marathon, not a sprint. I don't think the company is a good fit for someone looking for a stereotypical startup experience, like what you see in popular media. Finally, everything is optimized for people that are really into their work, so I don’t think the company is a good fit for people that don't happen to fall into that bucket.