The slide out system works great but it increases costs. If wiring three racks with primo equipment, it's not a big deal. If it's a single system, the time and even the added wire for the festoon is costly compared to a setup that you can rotate. And there's not always the height for the rail system. And the rails and trestles have to be stored somewhere.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
