Not very sturdy, and easy to ruin.
I only gave this a 3 because they are so fragile and have never lasted the 2 weeks promised. Never sleep with the device on your leg, as the gel dries overnight and removing the unit from your leg will destroy the silicone. I ruined one the first day I got it by leaving it on. If you get the amount of gel absolutely perfect, they work great, but it's always hit or miss.
Rating: 3 stars