I don't buy presets; occasionally I will download free presets. Presets are nothing more than a one-click means of editing and do not involve anything that you can't do yourself with all the sliders in LR. If I find a look that I like by just moving sliders, I will save that as my own user preset.
Presets are a great way to speed up your image processing when you find that you are doing the same tasks over and over. I have created a bunch from scratch.
I have downloaded some free ones. Some I kept because they were useful; some I keep because I have not yet tried them; others I deleted because I did not find them useful.