As the others have stated, 50 to 250 is a huge swing in the SMB.
There are a ton of risk factors involved.
It is nice that the company has a specific vertical that they are able to service, but how long have they been doing it.
How is the software actually written? How is it served? How is it kept up to date visually? How is it kept up to date technically?
You might not be a developer, but you need to know these types of things when you go work for a software company. These are the things that will keep the company in business or drive them to their competition (or spawn new competition).
Great points right here. Last position I was at was considerably outdated and weren't getting up to date very quickly. Due to this they were gradually losing clients to competitors. Being that they had literally the one product when I left they were in a scramble to get up to date. Being aware of how development is going, languages being used, approaches to other tech will help you get a grasp on what you are getting yourself into. There's a difference between getting paid 20% more to join a team or paid 20% more to save a company from going under.