This is generic info, not specific to your request...texture on the bottom of the tub can help from a safety standpoint. New CI is pretty smooth. Throw in some slippery hair conditioner and soap, and it can get dangerous. As an aside, even if you aren't planning to install any safety bars in the tub/shower area now (it's not a bad idea), while the walls are open, have the contractor install cross braces/blocking where you would be likely to put them - take a picture with a yardstick showing where they are. Then, should you decide you want to add in some safety bars, you won't have to worry about trying to find the studs as you'll have a horizontal reinforcement...they could go anywhere along that line. And, since it seems they don't make the silly bars an integral of the typical spacing between studs...this will let you get screws solidly into them and let you put the bar anywhere you want (within reason). There are fasteners that will work to hold bars where there aren't fasteners, but if you did look for a stud, and were only close, you may then not be able to use those, either, since they need room to spread out and a stud to the side would prevent that.