Boolean - true if the set was equipped, nil otherwise. Failure conditions include invalid arguments, and engaging in combat.
local name = GetEquipmentSetInfo(1);
local ok = UseEquipmentSet(name);
if ok then
print("You're now clad in " .. name);
This function does not produce error messages. FrameXML/EquipmentManager.lua provides EquipmentManager_EquipSet("name"), which will provide the player with an error message if the equip action fails (but does not provide you with a return value).