I purchased the 750SL several weeks ago and have been running it hard since then. It easily handles three layers of 9 ounce Latigo, even when I just tap the pedal to advance it one stitch. My 1 hp Consew motor struggled with this and often just stopped. The real challenge for me is sewing relatively slowly through 7 layers of 21 ounce duck canvas. The Consew always bogged down, but the Kinedyne handles it without any sign of struggle, even with a 23 needle. By the way, this is on a Juli 1508NS.
What I really like about it is that the needle stops pretty much on a dime when I take my foot off the pedal when sewing fast. My other motors seem to give way to momentum and allow the machine to sew up to three stitches before coming to a halt. It’s as if there is a brake in the motor.
I can’t speak to durability since I’ve had it such a short time, but based on the first few weeks of use, I highly recommend this an an alternative to a speed reducer, especially given how well the needle positioner works.