That's what I've been using. It gets the job done.
Ladders, they can get me into the trees, and I can make my way up from there, but there are a lot of instances where the ladder will not do. For instance in trees where there is a gap from limbs that I can reach by climbing with no ropes or spikes to limbs that can't be reached by climbing without a rope and harness.
Thus far I've actually only encountered one tree that I could not ascend the whole thing with out extra help. I took 10' inch spikes, and made steps to reach the crown. Tree was a removal.
I have encountered jobs to do bids on where the trees were the real statues of liberty so to speak, but of course I had to turn down those. Some of the customers asked why I would turn down the work.
I look forward to taking on those jobs in the near future as long as they are not over any structures for the first string of them.