Product review (5 stars): So tight that no filler was needed.
I ordered three of these for our butcher block countertop.  They worked great!  They are holding the two pieces we had to join very securely. We were able to pull two pieces tight enough that we didn't have to use any filler in joint at all. I will say they are much easier to install before the countertop is installed.  However, we have an old house with uneven walls, so in order to install the countertop, it had to go in in two pieces. That meant they had to be installed after it was in place. They still worked great. It just took a little more hand coordination to install them.