If the milk flows good when you are hand milking, how long can it take to milk out a goat? Sure, you will get tired and sore at first, but in a week or 2 you will not even notice it. Plus, when you add in the time it takes to clean the machine and all, hand milking is as fast or faster. I honestly cannot see using a machine for one goat or one cow unless you are not going to be the one milking all the time, and will need others to fill in for you.
I went from milking 2 cows , to milking 4 cows twice a day when I purchased 2; off a commercial dairy no less, so they were making more milk at later in their lactation, than mine were at 60 days fresh. The first 2 weeks were murder as I had more muscles in my arms and hands just screaming with the pain and exhaustion. God bless the last cow, patience, when I got her done the first 4 or 5 days. But I got used to it. I get tired now when milking because I don't do it all the time, but as soon as someone comes fresh and I am back to it, my muscles will complain for a few days/week then do fine. I cannot see where milking a goat that also has kids getting some, could be that bad unless she has tiny teats or the orifice is so little as to have a small stream of milk.