I've used Parse and would do so again -- I also use other stuff. They are excellent for getting up quickly and "it depends" on whether they are ok for scaling. Personally, I worry about fixing that when/if it happens.
I've been assuming the scaling is taken care of by these companies but I could be wrong. I guess the price would be my number one concern at scale.
Then, if it make sense at some point to try to reduce that cost, you can replace it.