This paper discusses recent developments with the two-stage MIMO OTA test method. It first introduces the concept of the radiated two-stage (RTS) method which is based on a first stage of antenna pattern measurement followed by a second stage of throughput measurement using a signal generated by convolving the device antenna pattern with the desired spatial channel model. The resulting signal is applied to the DUT either through a conducted or radiated connection. The radiated version of the two-stage method was approved by 3GPP in Technical Report 37.977 v12.0.0 [1]. The primary advantage of the RTS method is that arbitrary 2D or 3D spatial channel models can be emulated using a low-complexity SISO anechoic chamber. The potential extension of the RTS method to active antenna systems was covered in [2] and the development of the antenna test function (ATF) defined in [3] was covered in [4]. Measurement uncertainty analysis for RTS is provided in this paper including the impact from degraded isolation level and antenna pattern error. This paper examines recent measurement results and the insight that can be gained for device designers by examining the antenna patterns measured with the aid of the ATF and also the many signal metrics that can then be calculated in order to predict and explain device performance. Such insights into the underlying reason for device performance are valuable to device and antenna designers and are only possible when using the RTS MIMO OTA test method.