It's been pointed out by several developers that he doesn't use any best practices (such as DataWriters in XF1 or Entities in XF2), and he throws random queries that don't even do anything but load a bunch of garbage data the never even touches into controllers. I'd be scared to see the performance of any site that uses any of his add-ons that do anything with any sort of data.
Just for an example, not using the DataWriter for a lot of things he does (An example being his add-on that converts img tags into attachments) will break any other add-on that does anything with attachments. For example, I use Goodie2shoe's add-on that runs attachments through kraken, doesn't work if you use Andy's garbage add-on because he doesn't use a datawriter, so no other add-on knows that it exists, he just randomly inserts it and then tells people it's a server issue when shit breaks because of this.