I was first a little turned off from this tool because it appears to have sort of a cult following, similar to Apple or Tesla, however, after using it I guess this can be justified.
To put it short, I really do love Jungle Scout. Before I got the extension, I didn't know how many units each product on Amazon sold each month. That information is so important to know so for that reason alone, its a no brainer.
And, even if you don't want any of the Jungle Scout tools, their blog and free resources are top notch.
I don't think I'll join the JS cult anytime soon but I do recommend it to anyone I talk to.