Pros
I worked at Spark451 for 2 years and found it to be a tremendous learning opportunity. The small size of the company facilitates interaction between multiple departments enabling driven individuals to gain a wide range of experience. The work is fast pace and the employees young. This is a fun, exciting company for a recent graduate. However, it's also a great company for one seeking a long term position. Spark wants to see its employees grow and makes a conscious effort to hold on to valued individuals. From my experiences, a quick learner who is motivated and not afraid to self-advocate would be an ideal fit for the Spark team.
Cons
If you're not self-motivated and organized one could get buried under the heavy work load. Also the degree of managerial oversight varies depending on your role, which is a pro or con depending on personal preference (definitely a good thing to inquire about in an interview). Spark's company culture is young and fun, but employees are expected to carry their own weight and workload is strenuous and deadline driven. All that being said, work/life balance is significantly better than companies based in Manhattan.