Digispark Attiny85 dev-board - Program via USB or UART/serial converter?
Having bought several of these units from several sources:

They are typically pre-programmed, and should work out of the box with the Arduino IDE. I have not yet come across one that doesn't have the USB bootloader.

However, because they come from so many suppliers, this may not always be the case. In which case, you should get yourself an AVR ISP programmer (they are very cheap), which can program any ATtiny or ATmega.