I know it's a practice that comes from the Germans and I think it's well thought out. I find that it brings together the life in a herd, food adapted to each one and spread out throughout the day. The horses are housed in two herds of equivalent size. What essentially differentiates them is the mode of feeding. This one is in connection with the more or me great homogeneity of the flock.
For the criteria, I am not an expert, but I would say that the number of horses can impact, because it is a stable that works more easily with several horses (I think it is not interesting to do it for two horses). But the biggest criteria are the facilities! Both parties have access to a concentrated, individually rationed and fractionated food during the day. Access is controlled by an automated system. Each horse is equipped with a collar or an implant at the neck that controls its access via a centralized computer system. The difference relates to the feeding of hay or some have access to the hay via islands whose access is periodically open during the day so as also to split the inputs. The other accesses the hay in an individual way and when the allowed time has elapsed, the access hatch goes up slowly to encourage the horse to leave.