It's a function of you and your environment and experiences.
Back story: I have had a Part 61 CFI and AGI for 30+ years. Most of my students are engineers, technicians and scientists. Almost all of them have studied from a review book, one or two general texts, and the FAA material. I spent some time tutoring them, but for most of them, it was very minimal.
Today the sUAS study materials are better than some of the older test prep books that my students bought. I seldom help anyone with a UAS issue, but if I were I would be telling most people to just use the freebie materials out there. Most of the free youtubes are OK, and most are correct.
If you are uncertain, you might find a study buddy.
However, if you tend to need coaching while you are learning, and you tend to be frustrated by researching out answers when you are stumped, then the cost of a course is likely well spent in that you will be less frustrated.
If additionally, you tend to not test well, considering the cost of the test at $150, then paying for a course reduces your retake risk, and I would suggest that.
In summary, if you are good at independent work, or have a study buddy or other resource, then you can readily do things for free. If not, you may boost your confidence and your chance of a first pass by buying a course (~$150).
If you know nothing about the field, and you have to get the 107 certificate quickly, and you have good funding, then sign up for an in person course which gets you classmates and an instructor and has a goal of completing your training in a couple of days.