I have had a very good experience with Crowdbotics thus far. I contracted them to build a dropshipping application that was beyond my ability to create and would have been very challenging to create with only one or two freelancers. Having a full team at your disposal is invaluable while building a complicated application.
I did my research and felt like CB was easily the best bang for my buck. They were able to quote me $70k, other agencies were quoting me well over $100k, and up to $150k, to build my application.
When building an app with many features it is easy to miss things when creating the beginning scope. Make sure to leave some room for possible budget increases. I think many of the negative reviews here probably did not scope out their app accurately and it led to increases down the road. CB always did a good job of describing why they would or would not be able to perform additional work on the app that sometimes was a bit ambiguous in the initial scope.
Overall I have had a great experience with CB during the course of my app build. We are getting very close to launch and I am considering signing up for a Care Plan as I do not have the resources in house to manage an application like the one they built for me. I will update this review in the future and provide details on that experience.