Possible dangers of home fermentation of vegetables

I bought this FARMcurious Fermentation kit on Kickstarter. Once I got it and started making it I found their claims of it being "super easy" were a little exaggerated. When looking around online I found that other people recommended weighing your salt instead of measuring by volume and that it absolutely did matter what kind of salt you used (so I rinsed the veggies off and started over).

I started them fermenting in August and was supposed to check them in October. Well, it's now January and I've just been too afraid to try them.

There is no mold growing, they've been in a dark room in my basement. The airlocks are all intact. Nothing "looks gross". I opened up one that had pickles in it and it just smelled "pickly" (not bad at all). I tasted one and it was just sort of soft-ish and very salty. It's been 2 hours and I'm not dead or sick or anything.

My question is... What are the dangers here? How would I "know" if it "didn't work" or if it "went bad"? This person tested PH and looked at it under a microscope. What would I look for exactly? What would happen if they were bad and how long would it take to happen?

Most stuff I've seen online claims that if it were dangerous it would smell so bad you couldn't even eat it and that this is the absolute most safest method of preservation.