They are not nearly as strong as wing tubes. You only have the strength of a few bolts and the shear strength of a glue joint for all of your spar carry though strength. I have never seen one fail but I never really trusted them. The retaining bolt tends to strip out also.

I have a big SIG Spacewalker project scheduled for next winter and I'm changing out the SIG system to wing tubes. I even find the tubes much easier to install.

Byron used the same system as SIG's for years. I did see a couple of these fail with catastrophic results.