I had the same experience as Karin. I too had a set of Powerblocks on the lower end and I too gave them away. Too many of my clients found them cumbersome and thought that they looked like too much weight. The thought that they might be heavier worked against them, as the mind can often trick the body. I ended up buying some individual weights in various weights.
As an in-home personal trainer, I personally liked the ease of transport of the Powerblocks. But since my clients had such negative reactions to them, I didn’t find them beneficial to our training sessions. Now I just keep a trunk full of varying weights depending on who I’m training and what their session goals are for that day.