we use velcro on the clew of the main instead of a slide because it does seem to slide a bit better than a slide ... but velcro doesn't do all that well in sunlight as we see down here in FL. New piece every year is required. With a pole left out in the sun daily ... I wouldn't use velcro.
However lashing, using a decent rope, has worked for thousands of years. I was impressed with the photo showing how Fuzzy Wuzzy uses it on the boom to attach the main sheet.
Related: remember that most booms break at the attachment for the vang, and that should tell us something about hard attachments at mid points.
