Hello, I use OTG and iphone, it seems to be by far the best way to use Spark..  The only bothering thing is the need to plug in the OTG USB cable after turning on the RC, everytime!
Let's suppose you are doing something that requires more than one flight, you turn drone AND RC PFF between flights, to save power....
If you turn RC ON again, the iPhone does not notice that a device is plugged in, you have to physically unplug and relug the connector!!
Moreover, if you do the same at iPhone cable's end, it does not work...  you MUST act on the Micro-USB end!  The RC female connector is starting to get loose, and this worries me a lot...
P.S.  With Mavic and it's RC, the iPhone "catches" it as soon as you turn the RC ON, it should be like this, isnt't it?

That's the only way on IOS!... On android you don't have to plug in and out, OTG it just works.