Progressive vs. Direct Connect thumbs ,
Progressive Style = the thumb cylinder attaches to added linkage provided with the thumb , much like the OEM bucket idler linkage, in turn that linkage then connects to the thumb body. Some New Style Progressive Thumbs are currently out that use a universal type "Rocker" Linkage.
Progressive Style Thumb Advantages = In most cases added thumb travel or rotation is gained with Progressive Style. Some companies will claim added clamping pressure is gained, our computer models do not support that claim and I would not say it or buy it. I feel an overlooked advantage to Progressive is with the linkage used between the cylinder and the thumb the cylinder is pushed further up the stick keeping the cylinder rod out of harms way. Your expensive cylinder is not exposed to rocks, dirt, mud and water as much as the Direct Connect style would be.
Progressive Style Drawbacks = Higher purchase cost, added weight, additional moving parts and pivot points needing maintained. Linkage parts on some thumbs are machine specific and may not be readily available. Progressive Link is only available as hydraulic operating.
Direct Connect Style = the cylinder attaches directly to the thumb body.
Direct Connect Style Advantages = Less expensive, Less moving parts. Less weight, Sometimes fits shorter sticks progressive thumbs will not. Direct Connect is available in mechanical, also called Stiff-Arm style. (No hydraulics required on the machine for Stiff -Arm = less $$)
Direct Connect Style Drawbacks. Cylinder more exposed to damage, may be less rotation or thumb travel.