Pros
1. The small setup of the office allows everybody to get involved in all the facets of the architectural projects.
2. The employer is a young and energetic person whose enthusiasm for the work easily rubs off on you.
3. The design philosophy of the firm is to be to dabble with everything, but not at the cost of quality!
4. The company ensures that all the infrastructure in the office like computers, printers are up-to-date with the current specifications.
Cons
The only Con that comes to my mind is maybe a smaller setup would not bring you in touch with a lot of people from varied backgrounds who work with you in the office (read - exposure) but that does not take away from the learning experience at all, since in a bigger setup one would not get to work on all the aspects of a design project.