Because such an object would not be much larger in dimensions than Jupiter, it would not be any brighter as seen from Earth in reflected sunlight than Jupiter, and could be less bright, if it was positioned in the orbit of any of the giant planets in our solar system. The rings could be several times as bright in reflected sunlight as the planet. And you need to research how much, if any, visible light an object with the mass of 10 to 40 Jupiters might emit as opposed to reflecting.
An object with a mass of 10 to 40 Jupiters would be somewhere near the transition zone between giant planets and brown dwarfs. The transition mass between the most massive planets and the least massive brown dwarfs is usually given as about 13 times the mass of Jupiter, but I think there is a considerable uncertainty about that.
The transition between the most massive brown dwarfs and the least massive stars comes at about 75 to 80 times the mass of Jupiter.
I believe that stars are massive enough to fuse ordinary hydrogen, while brown dwarfs are only massive enough to fuse deuterium, and maybe only for part of their lifetime.
So a brown dwarf would be much warmer than a giant planet, and might shine in infra red light, and possibly a little in visible light.
Curiously, planets much more massive than Jupiter, and all brown dwarfs, and the stars with the lowest masses, would not be any larger than Jupiter due to being much denser.
In fact, some are a little smaller in dimensions than Jupiter.
So a planet or brown dwarf no larger in dimensions than Saturn or Jupiter at the distance of, for example, Saturn, should have an apaprent magnitude of reflected sunlight as seen from Earth between that of Saturn and Jupiter. If this body had very giant and dense ring system, the rings might have a refelctive area several times as great as the planet and might be several times as bright as the planet in reflected sunlight, depending on the angles between the rings, the Sun, and the Earth. And you need to find out whether a brown dwarf in the mass range of J1407b, 10 to 40 Jupiter masses, would emit visible light, and if so how much.