These blocks are ideal for supporting parallel clamps when clamping square or rectangular projects during their glue-up. They keep the clamps from tipping over, keep them on the same plane, as well as provide additional space and visibility beneath your project all of which lessen aggravation and wasted time while the glue is drying. They are also ideal assets for edge gluing narrow boards to form larger panels. The four blocks will support two parallel clamps, so factor that in to how many clamps your project requires. The parallel clamp's steel bar will protrude a bit above the top edge of the block when using the block's upper slot, enabling you to clearly see whether or not your boards are lying flush on the steel bars.
The blocks work as designed but the clamps are not flush with the top of the blocks. I tested all my clamps (Irwin, Jet, Bessey) and non were flush. I think that this product would be much better if the clamp bodies were flush giving a larger surface area.