Pros
I worked with Dionach for more than 5 years and I am overly satisfied with the management and people in the company. I am a very people-oriented person myself, so Dionach was like a family to me, especially the past years before the company started blooming further. Even nowadays, although there are technical teams and so on, everybody works with everyone.
Apart from offering a good environment, the current structure helped me understand an infosec business from 0 to 100, I used to work with pentesters, the directors, business development/sales and the project managers, while maintaining close relationships with customers. To me this is invaluable as it means that I understand this type of business 100% now and has helped me improve my soft skills a ton.
Another great thing about Dionach is that due to the huge variety of services offered, if one is willing to put in the energy and effort they should get very good exposure.
Management take feedback onboard, something important to me, and consider everyone's feedback. Generally speaking, I think Dionach has great potential for further growth and publicity in the future.
Cons
Overall, I can't think of deal breaking cons to note here, but perhaps on disadvantage to consider is that although R&D is performed, there are not many huge R&D projects that last weeks/months. Of course in this case you are better off working for a research-based company.