This is an amazing product that has helped my small garden tremendously! I have used it for over 2 years now, in multiple gardens with different results each time (it's not like one size fits all). The main issue we had was getting proper soil moisture when using this system - but you can use your own solution if necessary. Also, be sure to get enough fertilizer inputs into the mix before planting so plants don't struggle too much once they're established. It does take some experience, but nothing complicated.
My biggest problem solved here would definitely be dealing with drainage issues while gardening outside.