The Ekkia Combi Training Aid can be used when lunging and on the walker, as it helps with hindquarter engagement,
Most training aids act only on the forehand and take away an important part of the horse's impulsion. This can be compensated by the rider's legs while riding, but it becomes a lot more difficult when the horse is without a rider. The risk is to obtain an artificial position of your horse, without engagement of the back legs, which has no interest at all.
In fact, the principal interest of a training aid is to help your horse to engage the back legs, this causing the back muscles to develop in order to obtain headset, balance, and a horse who give in at the poll. This is an important part of the training and conditioning of your horse.
Thanks to the design of the Ekkia Combi Training Aid putting a strap at the top of the hind legs, it helps with hindquarter engagement, and efficiently stops the horse from becoming "flat" and brings him gently and precisely on the bit.