These are ultra bright 140mcd! You can drive these with less current to get the same brightness to save power, or crank them up to 20mA and have them really bright.
These displays are multiplexed, common-cathode. What that means it that you can use a 74HC595 or just 8 microcontroller pins if you can spare them to control the 8 anodes (7-seg + decimal) at about ~15mA each, and then connect NPN transistors or a TPIC6B595 to the cathodes to sink the 8*20mA = ~120mA maximum per digit.
These come in a bright green color, we also have red and yellow
Dimensions: 0.508″ x 1.582″ (12.84mm x 40.19mm)
The datasheet has lots more information on BL-Q39A-42UG-21