I'm not a huge deep sea fisherman but have spent some time out there. It does help some with seeing the fish and the higher they go the more help they provide. I have been up on one that was three levels high and you can realy see alot like grass line floating objects etc. Most are just one level and they real help with watching the lines and everything going on and they give a great view of a billfish hitting the line.
it makes a huge difference. i have never used a true tuna tower offshore but use a tower regularly inshore when spotting cobia and it makes you wonder how you did it before. you really notice the difference when you are yelling to the people below to look at something and they never see it. the basic idea is just getting a better angle on the glare on top of the water.