I participated in Calgay's playtest on the 11th; it was stated quite clearly at the beginning that a primary goal was to test Bind Legs for safety concerns, and it was also state quite clearly that any safety concern you had as a player should be voiced.
I had my legs bound, obviously.

So did nearly every other PC on the mod that was set up to test Bind Legs. Even as a player who rarely enters combat, I didn't feel unsafe to have my feet planted. I was given about a second or so to get stable with my feet where they were (my fighting stance can use a great deal of work, but my feet were a comfortable distance apart when I was affected and this consisted of a slight shift of my left foot to be angled slightly more forward than it was), and then continued to fight. It didn't end well for my little Artisan swinging for 2 and my backup busy with their own fighting, but I didn't feel unstable or otherwuse in danger of falling down.
I will note that I was engaged 1-on-1, and the NPC didn't circle behind me to attack, but I will also note that that also no point would I have considered attempting to twist my torso to defend from such an attack. I don't consider that to be a safety issue with Bind Legs itself, as I feel a huge draw of the spell is allowing attacks from behind to land consistently in the absence of a more direct threat to hold the target's attention.