Not a fan of any phone or tablet app at this time, here's why I say this: the additional device is a liability - you find it forgotten, lost, or stolen - you're out a monitor.
The other side of it, depending on the area you're traveling's texting laws, it can easily be seen by the LEO your distracted by a device. As well as some of these are displaying upto 20 PIDs at once, with few exception drivers, that can become an information overload.
As for the CS vs CTS debate, its a matter of perferance as both will display a max of 8 PIDs. The CTS has a larger touch screen, and the ability to have a back up cammera. I run a CS.
If you really want data logging, I like the AE software via a laptop. This is something I'm looking into now, to add to my truck for modification testing, and troubleshooting.