I also use a Shure mv88 and it pulls nice stereo recordings. Of course you get the best results if you're not too far from the source.
Big drawback is the impossibility to charge the phone / iPad while recording. Not a big deal in audio recording, which won't draw too much juice, as you can record with the screen off. Different if you shoot a video, either using the stock camera app or the Shure video app; I couldn't find any video recording app allowing to set the screen off while shooting. The difference between audio and video is really huge, I suspect more because of the screen on thank the recording thing itself. No workaround for this limitation; Apple usb3 to lightning adapter doesn't work as it can power iPhone/iPad through the lightning and accept an external device via usb, but can't do the opposite. Shure released the mv88+, which is essentially the same mic but with a different design, allowing iPhone charging as it can be used with the summentioned Apple adapter, but mic+adapter makes roughly 250 euros in Europe which seems a lot. If you are prepared to charge externally you may as well end up buying an audio interface which allows you to choose any mic you want and link it to the iPhone / iPad so you can get even professional sound directly with your video.
Apart from this comfortable use, I don't see any particular advantage of using an apple device over a recorder in order to pick only sound.