If your 40 minutes of driving for every 90 minute lesson is accurate, you can be honest and say you don't think you're getting much for your money as you're getting less than 30 minutes of driving per hour, and that your friends instructor offers much more driving time.
There's no reason you can't talk while practicing, and if you wanted a lecture, you'd look for one on YouTube.
Driving instructors are in a difficult situation with fuel prices as they are but if there's someone doing a substantially better deal, you're obviously going to go for it.