Considring installing "sun tunnel" for light to dim area. Whats downside & how much light can I expect?

Hi, I Installed the exact unit you are talking about in a bath room in a garage apt in Texas. I had concerns with heat gain and all but wanted natural light in the shower. The tunnel generated lumen equal to about a 75 watt bulb. No Heat gain or ac loss and beautiful light for the fern my wife placed underneath it on a chain. It is an easy install and well worth the work.