How do I ensure this stick on will really stick?

Here’s one that’s actual stick on, which, if I were you, I’d stick it on to the wall outside the shower.

The others, like for example the one you linked, are not stick on but they’re suction, and the suction should lastl a long time but might not always stick.

https://www.amazon.com/GwernKB-Waterproof-Showerhead-Adjustable-Conveniently/dp/B0CP7V9PCJ/ref=sr_1_7?dib=eyJ2IjoiMSJ9.5HjrWGv2beTFPgVdRCdwSDBq6CobND2tqSse-ItngDD9qn7vUvPmKKfEeXo9fxCqq1JeLCykWw9spNVPpRO6ynmZTYsnWo5PoAoHHEAP5radxDoNdCrChiUf81qU3Ev675bmxIfEzGc2AjnktoA-J22_twLb-7NcXf2YCsrVmjngL1S__daCHphxwDpX8-TGJX9haXL3LNy9be0NjWBzO5VckOE3BnSDGRHKcJCSnE9GBL-mTuabeabZF5v3S_01WVZnr3d5npFPFXS4MzO1PzMeybh1r2IZwrBF4i4zx8-7akjV2ZJddaHPTu_uX39gMA6R2axp3A5iftJdLVoPx5AqXzH6wXlHxE4rYjwVZVf1J3bljd1b-KTNC0A9bAR9G_UM4gS9UA48ZDQGCXVcPZ6dyrY448JlneVZZcCM8hj3aGq6wtN_Jc3M0zT-8mhi.HxFH7ehF_nptiI-jSkldGuVGWOGrGCkHbu-OwkGv5Zc&dib_tag=se&keywords=hand%2Bheld%2Bshower%2Bhead%2Bhanger&qid=1735316329&refinements=p_85%3A2470955011&rnid=2470954011&rps=1&sr=8-7&th=1

Edit to add the one I linked is less than half the price of the one you linked.

You are right. I missed the suction part. I’ve dealt with suction handholds in the shower and I don’t want that.

I want something that I can securely glue on to the shower wall, several feet below the current shower head holder, which is screwed into the sheetrock just above the top of the wall.

^It’s important that you can trust what’s holding it up.
I had to use a shower like that after my transplant, and once while I was washing my hair with my eyes closed the shower head/handle fell and smashed my head. I was surprised how much it hurt me. I’ve had beer bottles broken on my head, but that stainless steel shower head, really concked me.

LOL! I’ll make sure Brothers Grimm!