I’m a GTD person, and have used OmniFocus since the beginning. While it is highly structured and can be difficult to learn, this is because GTD itself requires some serious orienting to a new way of thinking. GTD is not for everyone. But if you really “get” the GTD idea, you’ll find OmniFocus manifests it very accurately. I use the “PRO” version and if you want to really do GTD and be able to customize to your needs, you’ll have to go Pro. Whether the cost is appropriate is a personal decision. But I think it definitely is, mostly because Omni has OUTSTANDING customer support. When you have a problem, you get a rapid and thoughtful response.
I would give this 5 stars as the program has been of incredible value to my workflow, but I believe there is one serious issue, however which is Omni has a protocol that will drop a device if it doesn’t sync in a while. My guess is this is a security technique, but depending on your usage, it can be a glitch for your workflow. For example, I use OmniFocus on my Mac and my iPhone 6. But I mostly use it on my Mac. I recently had a reason to not use my iPhone for a while, and when I tried to sync, the system had dropped the iPhone from being recognized. This meant I had to go through my HUNDREDS of action items to figure out which I had added to the iPhone so that I could re-add them after syncing with the Mac database. While the company gave me good suggestions for how to avoid in the future, I wanted to issue this as a warning to others: if you sync between devices, do NOT let more than a few weeks go by without making sure all your devices are synced. The fact there is no warning sent to the user that his iPhone will be dropped without his permission downgrades the experience to 4 stars for this otherwise great product and great company.