Pluspunten
You may have a chance to touch all sorts of hot new technologies. This company has an above-average chance of giving you some much needed keywords on your resume. You will get opportunities to see multiple variants of full Big Data software stacks, and compare their strengths and weaknesses.
Both the CEO and the customers are technical people who dislike excessive marketing BS. The product is used by the Devs and IT groups of other companies, so customer bug reports are much easier to read. The customers make buy-or-reject decisions according to highly-technical standards.
Minpunten
OPEN OFFICE ENVIRONMENT with no environmental noise cancellation. This will drive a lot of people insane, and may even cause physical harm due to stress from the environment.
Nearly all process is improvised, everyone is in "immediate" mode where things are done on a basis of who can grab who at any moment. This is despite the fact that it is an enterprise software company that is supposed to produce reliable and stable software.
If word gets around that you are competent, then everyone will immediately try to pull you into everything. The top talent seems to inevitably leave, sooner or later. It's one of those kinds of environments.