Hi nhdevildog,
Spurs are the quickest way up a tree. However, spurs on a living tree are like getting a tatoo with dirty needle. It contaminates a living system.
I did tree work for a short period. When climbing was tough, spurs were the choice. That was 25 years ago. There are techniques and climbing gear that are better for a tree.
I understand that you're making a choice that affects your job. Spurs get the job done. Just know that it's not the best thing for the tree.
www.treebuzz.com is a good site for you to check out. They have a forum on tree work.
Good luck!
Regards,
JimK
Keep FIT - Fun in Trees