I see no advantage to having both. Why don't you switch your trim for one without a diverter? I frequently use the iBox with just a hand held on a slide bar. The outlet, valve, and slide bar are lined up vertically in one line, with the outlet at the bottom, valve in the middle, and slide bar above. The shower head itself is offset from the bar due to the bracket that holds the shower head, and the hose hangs down from that (offset to the side of the bar and valve) and loops down and around to the outlet so the hose is not in front of the valve.

Thanks for your thoughts, catbuilder. Yeah, you're sharing my sentiment. We are using thermostatic trims, where the temperature control is on one knob, and the flow rate is on another knob... the flow knob can go left for one outlet and right for the second outlet. We are thinking about changing out the trim for one that only controls one outlet, though would want to find one with separate temp control (always get the same temp turning off/on). Alternatively, since we may add a fold down teak seat for older guests near the entrance to the shower (opposite end from the shower head), we might think about using the second zone to control another wall outlet and small hand shower there... I still have to process if that would be odd.

We did a little mockup this morning and are not a fan of having the actual showering head offset from center, so I think that instead, the valve and outlet may get offset to the right a little with a shower niche balancing it on the other side.

A layout akin to the below pic is what we had in mind, but with the outlet in place of the diverter and a shower niche same offset to the oppisite side as the valve. The only drawback I can think to it is that if someone ever wanted to conver the shower to a traditional shower, they would have more plumbing to contend with.

We have rain shower heads combined with hand held hubby like the rain shower better for a nice shower but uses the hand held to rinse his hair and also spray down the walls before he squeegees I think you get what works for you.

It would not be odd to have a separate hand held shower head at the other end of the shower, although I would probably use a separate valve for that, especially since you are talking about elderly guests using it. What I find nonsensical is to have two shower heads in essentially the same spot.

Why are you worried about some hypothetical person at an undetermined time in the future that might or might not want to change the plumbing? Is this not a traditional shower, in any case? The hand held on the bar functions as a fixed head, no one has to slide it up and down.

Ok, fair enough. "Why are you worried about some hypothetical person at an undetermined time in the future that might or might not want to change the plumbing?"

Probably because in rebuilding my house, I've found so many issues I've had to remediate - code compliance, structural, and then just the ones that make you scratch your head and think 'what the hell were they thinking'. Some, pretty bad stuff, like the roof not structurally connected to the framing when the idiot contractor converted to cathedral ceilings. I don't want to do those things that make folks scratch their head, and am probably just overthinking it :)

I had suggested the valve along the 5' (longer) wall of the shower, accessible both from bench and primary showering area, but my wife didn't want to 'wreck' the look of the cool large format tile going on that wall. So, I think adding a second valve there will also be shut down. That said, our parents live out of state and don't visit that often, but would also feel bad if we didn't make it a shower that 80-something year olds can use comfortably. It seemed like a step up from having a long hose on the main head. Then add a small volume control valve like this at the head:

Grohe universal volume control valve for shower heads

I like to do two separate fixtures with separate thermostatic and volume controls ... assuming you aren't in CA where they can not operate at the same time and must have a diverter.

My experience is that the handhelds don't produce the same pressure as a wall mounted head ... the water does have to travel down a hose an extra 5 ft.

I like to use a Speakman Icon fixture for the wall mount and a Jaclo handheld/grab bar with the pivot joint attachment for holding the handheld fixture.

The pivot attachment pulls the handheld away from the wall and allow you to aim the handheld in any direction, specially all the way down. Most handheld systems are too close to the wall and don't allow you to pivot the handheld to the best angle.

Here is the set-up in one of my guest bathrooms. I have a standalone teak bench on the left side, behind the pony wall.

Close up of the Jaclo pivot attachment (not standard with the bar and has to be specified separately when you order).

The problem isn't the extra 5' of hose, it's the shower head. Get a good shower head and you won't have a problem. Don't believe it? Just look at all the posts with advice to put the valve at the entry, nowhere near the fixed shower head, so as not to get blasted with cold water when it's turned on. No one says, "don't do that, you won't get good water pressure". Hand held shower heads get a bad rap, but the bad ones are no worse than the bad fixed ones. The good hand helds are just as good as the good fixed ones.

To each his/her own, I guess, but personally I like a good large fixed head with a handheld sprayer. I just installed a huge rainfall showerhead with a handheld and I'm really happy with it. With my set-up the handheld is secondary - honestly it's more for cleaning than anything else (and I'd use it for rinsing my hair if my rainfall shower wasn't up to the task, but surprise surprise it is). I don't think you can get the same kind of spray coverage from a handheld. I also (personally) don't want to keep fiddling with my shower head so having it be on a bar/movable would not be advantageous for me. But YMMV. If it were my house, I would install 2 heads. I guess I don't see having both as a disadvantage.

We only have a handheld on slide bar. It works as a fixed shower head and then can be handheld. My husband likes his shower head up high and I like that I can lower it for me. I see no need to also have a fixed head.

Having both is way more convenient than just a hand shower.

We renovated our bathroom last year and put in both - fixed Roca overhead shower plus a hand shower on slide bar. The overhead is great for regular showers when you just want to stand under water. Hand shower is useful for washing kids, cleaning the tub, or when you don't want to wet your hair.

If you only have hand shower, you're either holding it the whole time (annoying) or docking it at fixed height, which defeats the purpose. The combo gives flexibility. Quick shower? Use overhead. Need to rinse something? Grab hand shower.

Only downside is slightly higher cost and more plumbing work.