We present and demonstrate a highly stabilized non-isolated single-mode Brillouin fiber laser utilizing a novel, simple, and inexpensive approach for locking the cavity length. Our scheme is based on an intuitive control algorithm programmed into an embedded microcontroller and is characterized by smooth control signals. The laser cavity length is controlled in real-time using a piezoelectric actuator according to the pump level inside the cavity. Using this control scheme, we demonstrate ultra-stable, non-isolated, Brillouin fiber laser with power variations of similar to 4% and lasing frequency drift of few hundreds of kilohertz. To the best of our knowledge, this is the first comprehensive report on the frequency stability properties of controlled BFLs. We compare the stability of our laser to non-controlled cavities, investigate the impact of minimal isolation and discuss various parameters that affected the achievable stability and govern the laser short and long term stabilities. The demonstrated approach is highly attractive for real-life, out-of-the-lab applications where sufficient thermal and mechanical isolation is difficult and expensive to obtain.