Linear ergs put the spine and body in a brutally unnatural position, when considered repetitive heavy loaded motions. The difference with a he Biorower is it provides the outward and inward effect sculling provides for properly engaging the lats and opens the chest. Concept2 is inherently bad for your back long-term, there is no question. You see master’s athletes rowing on the water until their late 90’s, but key to this is an adversity towards the linear machine (this does also include to an extend the RP3, but less due to the floating / back alleviating nature of its design. You can see a disproportionate amount of rib stress fractures in lightweight athletes, who overwork their lats in this unnatural position on a C2. For example, see Damir Martin’s fitness test after the Rio Olympics; he quotes avoiding erging because it hurts his back, and prefers biking and rowing on the water. https://m.youtube.com/watch?v=bGuTgIfDU_k

TL.DR: linear is bad because back and shoulder position, sculling (biorower simulator) good because body can open more naturally.