From my experience there was a lot to dislike about SISU as a non-male, non-religious systems engineer and I very much struggled with the culture. I would estimate that during 70% of my time at SISU, not a single person would say even "Hi" to me over the course of the day. Most of the engineers were set on coming to work to work and socializing was not necessary. They would rather come to work to get their job done and spend their socialization time (including lunches) with their wives and children. This resulted in many lunches eaten in silence despite others eating next to me. In general, there was lack of camaraderie amongst my coworkers. But for full transparency, we were able to work well together when discussing our collective projects.
Once a week the company comes together for an office-wide lunch which sounds all well and good, if it wasn't filled with a lot of awkward silence. To start the lunch a Christian-based prayer would be said. As someone who does not share these beliefs, I found the practice in this day and age rather unusual. I voiced my concerns and was given the choice to sit that part of the lunches out which made for some very awkward mid-lunch entrances and looking in from an adjacent window to time it properly. To management's credit, they were open to receiving the criticism, but I would estimate that 80% of the engineers were Mormon (~12 total), so they weren't keen on ending the practice outright. And because of this, don't expect any office parties with local craft beers.
It being a small company you would expect it to be a bit more transparent with regards to the financials, but it never was. We would receive vague, "we are doing well" and "we have projects in the pipeline" without any clear understanding of our profit margins. Also, at the time you were unable to get 401K until you had been there a year which was a major disappointment.
And, in general, I did truly struggle with being a woman there having to endure some very awkward interactions with some people. There was a volunteering event which my husband joined me on and my coworkers chose to engage him in casual conversation but not me. And, as a small anecdote, I had the owner my first week there look at me eating a hamburger with shock and say, "You eat meat. I'm not used to women eating meat because my wife is a vegetarian." I didn't know how to begin to reply to that. Do you not know any women besides your wife? Maybe get out more? What an odd thing to say... Just talk to me like I’m a normal human being because I am.
As an aside, I have had 2 other full-time job and 3 previous internships in my career and have never had trouble making friends at work. This may be an outlier, but I doubt it.