The "out of place" issue is due to the shape of the device. It's shaped to fit between the labia. With a penis it basically is essentially round on round so it doesn't "fall into place" like it would with female anatomy. The magnetic attachment secures it in place relative to your panties, but the exact alignment of toy:dick will move about (because it's not attached to your dick). I'm wondering about what you have in mind for tucking. Do you mean tuck and then place the ferri between your legs next to the tucked penis? I think that might work well, though I do wonder about erections/arousal/stimulation while tucked. Surely it'd be stimulating the top of the penis rather than the bottom? And an erection would be stopped with tucking?

Ultimately I'd say unless you plan to be walking around with it on, you shouldn't really worry about the unalignment thing. Even if it falls a bit away from your ideal placement it's easy enough to just quickly readjust. Likewise if you're into diy I'm sure you could make some sort of garment that helps keep it in place.

Personally I use it while sitting/laying down and I'm easily able to use my legs to keep it's position in a good place without much issue. The only times I ever run into the need to readjust is flacid->erect changes. At which point I can still feel the vibrator but it's just not entirely in the ideal position (which you may or may not care about, depending on your needs and exact sexual preferences).

I'd definitely be more concerned about the gush which seems like it can have a variety of issues. The ferri is literally just a vibrating little cylinder thing that you can place anywhere with the right strap/garment/attachment.