Unless the shower area is very large, a lot of these seating options serve only to increase the dangers associated with using wet bathroom areas. Variation in the weight of users has also to be factored in, as well as any disabilities of users, both now and possibly in the future. I speak with much experience in these matters, as being disabled myself now, and have tried many of the options available. Most wall-mounted fittings end up being a point of failure at some time, allowing water ingress behind the tiling, etc. I've had to have professionally installed showers to be ripped out to repair water damage caused by the failure of such seating, causing major disruption to the household. Now I will only ever use purpose-made removable seating if it's needed at all.

If you do go ahead with any built-in seating, make sure it's built to cope with weights of over 20 stone or even much more. Remember, a large person falling can exert tremendous forces on such fitments, far exceeding the average quoted weight limits on some of these items, and these structures should take this into account. Nor should there be any sharp corners/edges anywhere.

On a personal level, I think that no shower area should be used without the installation of suitable handrails. Water and soap can lead to slippages, and maybe your old mother or grandma may be using your shower at some time, and you want them to be safe, don't you?!

Whatever you build, I hope it looks great and serves you well.