I often gig with two arranger keyboards, Yes it can be a PITA, longer set up/tear down, two OS to learn.... But for me it comes down to sound. My Ketron Audya has a sounds and styles that I just can't get out of my Yamaha 950 and vice versa. However sometimes I have time and or space limitations so I have to make a compromise and just bring the best keyboard for the job.

Here's a pic of a double arranger set up.

https://www.facebook.com/photo.php?
fbid=1212757075419504&set=a.153449051350317.28524.100000556690855&type=3&theater