It can sample and log much faster than 1 time per second.
By default it does it 5 times a second, for a human to looks at that is more than plenty:
#define BT_REFRESH_INTERVAL 200 //ms
It does no averaging for serial output, it only outputs the latest available reading.
The BT header serial can output very high bauds.
The baud rate depends on the BT module you use, or the receiver on the other end. The sketch default is 230Kbaud.
#define SERIALBAUD 230400 //Serial baud for HC-06 bluetooth output
See the firmware for details:
https://lowpowerlab.com/guide/currentranger/programming-firmware-updates/The log rate is determined by this parameter:
For proper use of external connected devices, please read the guide, you have to make sure whatever you connect to this header is not the same ground as the output negative terminal, that is why I suggest BT since it's wireless and has no shared GND with anything else. This is important if you measure current on any mains powered device, if it's a battery powered device, then you can even connect another arduino to read the serial from the BT header. Or if you have a laptop (running on battery, not plugged into mains), then that can also easily read the serial from the CurrentRanger USB port which outputs serial at USB speed.
And BTW - you can format the data in whatever way you want, the firmware is yours to modify in whatever way suits your needs.