The ease of use, how quickly I was able to deploy my solution in production without any issues! It is very easy for anyone with basic knowledge about programming languages (like me) or even non-programmers like myself who have no technical background at all but just want something that works out of box.
Nothing really specific so far though it's still early days - maybe more user friendly UI would be nice? We were looking into other solutions such as Heroku etc., which are not free if you need multiple instances/users. This one solved our problem perfectly since we only needed 1 instance per customer / account holder.