Mobile app development has grown rapidly, driven by the evolution of mobile app development tools, particularly Software Development Kits (SDKs). Developers from various platforms, including iOS and Android, share their experiences, highlighting the unique challenges and rewards of SDK development compared to app development. iOS SDK developers face more manual work due to limited support from Apple, while Android developers must navigate the highly fragmented ecosystem and diverse device specifications. Cross-platform SDK developers enjoy the challenge of working with multiple technologies but miss direct UI involvement. All developers emphasize the importance of understanding platform intricacies, the excitement of solving complex engineering problems, and the value of open-source collaboration, with advice leaning towards maintaining a beginner's mindset and extensive testing to ensure compatibility and reliability across diverse environments.