Pros
Lots of opportunities to grow. Projects are constantly evolving and you get to make a dent in software that's scaling very fast. This also gives room to experiment and test out libraries and programming paradigms. Culture is open and highly collaborative so expect answers to any question you might have. Products and processes are well documented (most of them), so there's always that to guide you (which is specially useful since the company is currently fully remote). Teams are very knowledgeable and the founders have a strong track of technical and operative successes. Expect the company to grow very fast.
Cons
Not exactly a con, but bear in mind that being a startup there's a lot of experimenting + trial and error. If you can handle (or learn to handle) uncertainty and challenges in an autonomous way, then you'll have a great time and learn a lot at Instaleap.