For a very basic application, these homegrown simulators are fine and will deliver fast time to market. However, as the complexity of your IoT application starts growing, you will need to put in extra effort to get the simulator to support all these features. Then, as scalability comes into the picture, you'll have to look into scaling the simulator instances, and it's orchestration. After all of that, you need to collect different results, measure different latencies, and the whole time, keep troubleshooting the simulator, which will keep getting more and more challenging.