The LensShifter (Balanced Focus and Zoom Grip for DSLR and Mirrorless Camera Lens) currently has a 20% off clip-on coupon at Amazon.com, dropping the price from $25 to $20. The coupon is easy to use, you simply press the green Clip button and the coupon is automatically applied. You don’t have to type anything. The discount will be reflected in the top right corner of the Amazon Checkout page. Here’s a screenshot if you are not familiar with Amazon’s coupons:
This is available in Blue or Red. With the coupon, the individual colors are cheaper than the 2-pack which goes for $45 and it is not coupon-eligible. These average 4.6 out of 5 based on 28 customer reviews. The maker is “Engineerable”, which also makes a Focus Shifter but there’s no coupon on that one.