Pros
Hopper gives you the opportunity to work on Valley-quality work on the East Coast. The product is consumer facing, in a fun category, and building forward thinking products. All of that and the great support it has gotten in the press—Apple Best of 2015, Google Standout Startup 2016, etc—makes for a really rewarding challenge. People are usually given a lot of autonomy to help make the company and products/services better. Coworkers are all genuinely interested in the company's success and they are fun to be around. Not to mention the offices spaces and locations make for a fun on-the-job experience.
Kontras
Hopper is a fast-growing startup, trying to become a company. So, there is a lot of messiness in process, communication, and logistics as these things work to get established and sorted out. Not unique to startups growing at this pace, but a hard transition to someone not familiar with startup expectations and speed.