There's even Grab booth now in airport in domestic arrivals, which I didn't use myself. Since I arrived in the middle of the night I had booked transfer via hotel, 40k for few minutes drive and we all know hotels always overcharge. When I was looking for my driver I was approached by a "official taxidriver", asked him for a quote to amuse myself, got a "very good price" of 300k
Took a Grab to Geger Beach in Nusa Dua the other day. No problems getting there but nobody accepted the booking for return trip, despite several cars nearby. Walked about 15 min and managed to book in front of some restaurant. Driver's English wasn't very good, but apparently "bad things" can happen if they try to pick up customers from the beach. And couple more drivers have mentioned that they would never go to Ubud.
Last year I stayed in Candidasa, was possible to book Grab/Uber there, but it sometimes took couple of hours. From Kuta to Candidasa was 200-250k with Grab vs 600+k with "honest hard-working" taxi driver.