Thanks for all the comments.
A comment concerning the possible damage to the wood from the metal probably needs some clarification.
If you view the YouTube videos you'll see that the neoprene pads supplied with the blocks can be attached to either side of the blocks to prevent ripples in the wood and reduce slippage. The pads are taped to the blocks or not depending on your preference. Any ripples on the wood caused by bare blocks can be removed by steaming them out with an iron and a wet cloth.
Please watch the videos for a demonstration. If you visit the blokkz.com web site you'll find links to the videos.
Concerning the price of the blocks, when you consider the ruggedness and wide range of applications for the blocks and that they may replace the need to acquire specialized clamps the price may not seem out of line.
Concerns over glue sticking to the pads this can be reduced by either covering them with masking tape and removing the tape as needed. Another method to reduce glue sticking to the pads is to spray the pads with a silicon spray lubricant. Let the lubricant dry before use. This will make removing any glue on the pads much easier and should not have any material effect on the wood which you'll probably sand before finishing anyway.