You aren't wrong that iFlash adaptors can be troublesome. I get the impression that RB devs have learned more about that than they would have liked to. And I've heard, but not from personal experience, that SSDs with a native ZIF interferface work more reliably. SSDs do seem to have a surprisingly high power draw, compared to the original 1.4" hard drives, though.
If you only need 256GB there's also the 240GB Toshiba 1.4" double-platter hard drive, but that now seems to be vanishingly-rare (have a couple and I'm hanging on to them!).
Main thing with the iFlash seems to be that the work to get round their limitations (failure to properly implement the cache flushing commands?) has the knock-on effect of increasing their power consumption, so I'm not sure the data in that linked 2016 article would still apply.