A feedback, that I give to many iOS developers: Please please do not start and stop the MIDI clock with the transport. This is not how it is meant to be. This causes trouble with hardware that needs it's time to lock on to the clock. The best way is to send MIDI clock permanently, and only send MIDI start/stop messages when the transport status changes.

I am aware of people, who do prefer a clock that gets started and stopped with the transport, so that any possible delays between pressing start and the actual start are avoided. There is a simple solution to allow both:

The default MIDI clock behaviour remains as it is, but Loopy Pro starts sending a permanent MIDI clock when Ableton Link is enabled. With Link the system waits for the correct beat anyway, and if one just wants a permanent clock, then it will just do this - even with no Link peers connected.