I had the same question and so wrote MyDigital's tech support. Here's the reply:
Not to worry, our drive definitely runs hot, but the main reason for that is because we put the heat sensor on the controller itself whereas our competition put the sensor further away on the PCB. You will not need to worry unless the drive breaks the 120c mark.
Douglas Hare
MyDigitalSSD
support@MyDigitalSSD.com
Also, a review on legit reviews com references the temperature of the Phison controller and that it is stable up until 125°. It begins to throttle at 80°. In their testing, hours of intensive RW activity never got the controller over 80, although it bounced right into the 70s.
I thought it was high, too -- glad for the 5 year warranty.