Yes, it's absolutely worth it. Loopline is correct, it's not an exact science but by using the same tool repeatedly you do get high accuracy in terms of whether your rankings are going up or down. I've also used Semrush's tool and as much as I like Semrush, I failed to find much of a difference in terms of the data. Yeah, they do fancier reports and the UI is nicer but then you're paying $79 a month and not $20 for life.
I would also mention that I bought Scrapebox for $50, or whatever it is, years ago now and it's an investment that has repaid itself many many times over. I find their support to be first class and very pleasant to deal with and when you have guys like Loopline putting out all his great content, it's a community worth investing in. The plugins I bought a while ago are being constantly developed and updated. So, paying $20 for a lifetime plugin that works with Scrapebox for me is a no brainer. The $47 offer that Loopline posted up is very good assuming of course that you don't have the others. The automator plugin is a real time saver.