It's an amazing site. Both the Spigot jars and the plugins on the site are great. Not to mention, the community is very helpful. I can't tell you how many times I've had issues I had no idea how to solve on my server and the Spigot community helped me out. Nearly everyone is very friendly. It's one of the best Minecraft communities there is. I definitely recommend it!
Spigotmc.org is a milestone of the minecraft server history. They do a great job for the community with their minecraft server modification. I use and trust this software now for years and thousands of other server do this as well. Including all big players in the minecraft server landscape. This website is also very safe to use. I never saw a bad/unsafe plugin download in the resources area.