In Wireless Sensor Networks (WSN), duty-cycled Medium Access Control (MAC) protocols trade off latency for energy efficient operation. Over the past few years, Wake-Up Radio (WuR) has been presented as the ultimate solution for this tradeoff, allowing to reduce both at the same time. However, this might not be the general case regarding the large range of network configurations used in WSN. Several previous works have been done comparing WuR to traditional duty-cycled solutions, but no one has investigated before the limitations of this technology. In this article, we analyze the benefits and drawbacks of using WuR in multi-hop WSN. We also identify black spots in WuR that have not been investigated yet. Our study is based on evaluations using COOJA, a simulator for networks of ContikiOS nodes. A traditional duty-cycled MAC protocol is also included in our study for comparative purposes. From our study, we quantify the performances of WuR and provide some guidelines on how this technology can be efficiently used in multi-hop wireless sensor networks.