Pros : These are fantastic for SO many uses...dams, weight, even sliced them into smaller pieces for smaller projects. You'll find so many other uses for them too.
Cons : Just wish they came in another weight that's a little heavier.
Other Thoughts : I got this thinking it was something else. It's heavy and chalky. It became useful when I needed to solder some odd shaped glass. I carved a groove into it with a screwdriver and it was easy to do. Since it is useful to me I recommend it.
Pros : This product works well in dealing with Soldering. Aluminum foil makes a great accompanyment (underneath) for any solder that might try to roll away.
Also quite light and portable for a 'brick'.