Thanks for the input. I have ordered the red bar. There is no doubt in my mind that the exercise is targeting the tendon well. It's just quite sore. However, it makes sense as I have played tennis for 40 years. I've probably damaged/healed several times over the years. I haven't had tennis elbow often though; the last bout was 6 or 7 years ago.
I am hopeful that the red bar will allow me to do the exercise more agressively through the range of motion.