I have been machine digging trees for close to 40 years. I have owned just about every brand. I am not familiar with the erskine brand. I primarily use Caretree and Dutchman tree spades. I do own an Optimal tree spade it has its place in nursery production but we cannot use it on certain varieties of plants. If you are just digging a few plants then the less expensive tree spades may do the job but if you need wholesale nursery production then the well known spades hold up much better.
I have noticed several nice tree spades for sale this spring. What size spade do you need and what are you planning to mount it on?