[palosanto]

Fair enough!  As the number of beats can already be arbitrarily chosen (in relation to the time signature) in the app the ability to specify an "On/Off/Emphasize" for each beat in a bar would give perfect versatility to configure the metronome.

For the time beeing I calculate the corresponding bpm value that gives me the beat 1 and 4 of an 6/8 rhythm and dial that in...

As I use the metronome in a live situation (as most users probably do) switching songs in two different apps is prone to errors and hiccups you might want to avoid playing live. It is better to simply tap one corner of the screen and have the correct click start....

Nothing to calculate ... Just do a 3/4 at 120.  It's the same.  The metronome doesn't care about the subdivision being a 1/4 or a 8th note unless you wanted also to emphasize the very 1st beat of the 6 louder than the 4th beat.