BasicMicro

My understanding is that since RoboClaw is a 5V device, it considers anything above 2.5V high and below that low. I tried using 3.3V microcontroller (Teensy 3.1) and it worked, but would this be reliable? Assuming the microcontroller gets enough voltage and current to get 3.3V out using its onboard regulator, would this cause any problems? I have a logic converter board from SparkFun, but I don't want it to take up space on the breadboard if I can get away without it.

Roboclaw is 5v tolerant. Internally it is 3.3v so its outputs are 3.3v. Inputs from the outside world are clipped to 3.3v. Signals at 3.3v or less are unaffected. Roboclaw considers any input over 2v to be a high signal so I doubt you will have any problems with the Teensy. Roboclaw has specifically been tested with 3.3v microprocessors(Arduino Due). You should not need any level converts when using it with a 3.3v microprocessor.