I would not use no bows under polos as they are liable to slip when the horse is in work.
I use the Eskadron liners, and if you look at warm up photos of most of the top riders, that is also what they use. No bows are not designed for when the horse is exercising.
This is one of the most used equestrian sites in the UK
Leg Bandages, Leg & Foot Protection, Horse-wear, Robinsons Equestrian
People over there have been using them for years with no trouble. Maybe we just had a better product?