I've run both without and with arm cuff straps.
Three things I've noted:
1) Without arm cuff strap usage, the arm cuff breaks over time on the Garrett's. I replaced two of them (one on my ace, and one on my AT Pro). I discovered that the reason the arm cuff breaks is stress placed on it when you're swinging. Basically, the physics of the swing results in your arm pressing against the inside edge of the cuff, which stresses it, and eventually causes a snap (about 800-1000 hours for me).
2) Using the arm cuff significantly increases the swing time. It may seem negligable, but the reduction of strain on your arm is real. I can go about 50% longer with the strap than without. That translates to 4.5 hours of swinging instead of 3. That's a huge amount for a simple contraption.
3) The strap actually stabilizes and makes it EASIER to retrieve your detector without using your eyes. Seriously. If you lay your detector on your hip, and slide your arm out, the detector never hits the ground. It just stays on your hip on the way down. Then when you're coming back up after the dig, you just slide your arm through the cuff strap, and the strap guides you to the grabbing point on the shaft. The strap is the lift point as you rise, too, as it carries the weight of the detector. Your arm sliding into the detector while you're rising. Without the strap, you have to grab the shaft, and get into a leverage point with your forearm (which is difficult, and results in you having to put the detector down, or deal with the up/down ineffectively). The strap actually saves me time and effort on the up/down, saving my shoulder, too. Without a strap, I found that I'd have to fully grab the detector (and the leverage point is awkward, unless you can get your arm in the cuff.
I'm a 100% of the time strap guy, now. It's much cheaper to replace a velcro strap than it is to deal with a broken arm cuff; I get to detect longer, and it's far easier to maneuver with the strap on, when you're up/downing.
