That is the type of set up we have as well and the one charging port on my double device (the one that is not the "rapid charge" one) still doesn't charge my iPad, just the phone. I don't know why, doesn't put out enough amps of the regular side I guess. I don't have a Scosche brand for charging, but do have a Bluetooth thing made by them for playing music through the car radio and it has worked great.
We also have not had much luck with cheaper devices. We bought a bunch for a space shuttle viewing trip a few years ago and they hardly worked at all and were just generally unreliable for charging our iPhones.
I recently saw some cheap colored chargers on QVC and reading the reviews, it seemed like about 2/3 of the reviewers said they were junk.