Yep, I'm pretty happy with Harvest. Even as a solo operator, invoicing is their most important feature for me, and I see TimeCamp only includes that at the Pro level (Harvest has it in their free tier). Cost isn't an issue for me, ~$100/year pays for itself with an hour of client work and it wouldn't be worth the time for me to switch just to save a few dollars.

I'd need to see more details about things like your Mac desktop app (eg screenshots, system requirements), as Harvest's Mac app is a big part of my workflow, also their integration with Alfred app on the Mac. I also like that Harvest pays attention to lots of really tiny details too.

It's probably not worth it for me to switch, but your link might be useful to someone else just starting out!