RP-1 Delay 4+

The Rotary slow panning preset sells this effect on its own - total spatial depth with a slight Doppler effect that’s unlike any other out there. There are undiscovered insanities in the app as well .. thinking the long dub delay effect.
Considering it does every modulation delay effect from flanging to chorus and vibrato, with the ability to create multiple instances of multiple effects through the AU feature, it’s well worth it.

For tape delay with all of the noise, flutter, and wow and ability to manually stop the reels in real-time, check out RE-1.

I use this on my guitars mostly. It has this beautiful stompbox kind of simplicity that I like but all the sound of a studio rack unit.
It works very well on acoustic guitars using the modulated delays

Recommended by me.

The app works well on my iPad Air 2 and is very useful to have multiple instances in various sound chains.

Apple needs to have a standardized way of saving AU presets with all AU apps and AU hosts so we're not recreating presets every time we create our own presets in a different AU host app (e.g. AUM and Cubasis) and it should not fall upon the developer's to come up with a standard because Apple has so far failed to do so.