The magnetocaloric effect (MCE) offers a promising alternative for environmentally friendly cooling technologies, particularly at cryogenic temperatures. However, overestimating material capabilities can lead to misguided research efforts and hinder technological progress. Metamagnetic materials undergoing a transition from an antiferromagnetic to a ferromagnetic state are often predicted to exhibit a strong inverse MCE at cryogenic temperatures based on magnetization measurements. This assumption is critically assessed here using Tb₃Ni as a case study. By employing a simple model and comparing results across various measurement techniques, it is demonstrated that the predicted inverse MCE does not exist. Specific-heat data reveal no evidence of this effect, while direct ΔT_ad pulsed-magnetic-field measurements indicate significant heating caused by dissipative effects linked to hysteresis. Furthermore, total-entropy calculations derived from magnetization data violate the second law of thermodynamics, clearly ruling out the existence of an inverse MCE. These findings underscore the necessity of complementary experimental approaches and a precise understanding of the transitions to accurately characterize magnetocaloric materials and identify suitable candidates for cryogenic magnetic refrigeration.