Come on - are you guys making maple syrup or knitting? By the end of the season your hands should be so tough and calloused you can dunk them in boiling syrup! Man up, Buttercup!!!
Just kidding - it does get hard on the fingers after a while, especially the metal containers because they get so hot quickly and the caps are smaller and have the dimpled edge. Cotton gloves work well as do rubberized ones. Blisters do happen - especially when filling a 35 gallon drum's worth in small containers.
After seeing this post and watching the Sensafill video yesterday I emailed Mapleguys about the system. It does work great on plastic jugs but does not work (yet) on metal containers. For glass they are coming up with a white plastic ring that needs to go over the bottle neck to reflect the laser.