Not sure why everyone is so upset over this.
I actually do think Knight will be a good fit in Houston, if he can every stay healthy. Ideally, he provides some upside off the bench at guard, can hit from three, plus has his moments getting to the rim. Never been a fan of Chriss, so I think thats addition by subtraction alone. Hes a solid buy low in Houston's system though.
Anderson makes a lot of sense considering the way the roster is currently constructed. Suns have more than enough defense right now. They need to keep building out the spacing, and Anderson will slide into that role quite well. Not to mention, if you play him with Ayton, the two can easily switch defensive assignments based on match ups. Suns have Anderson covered on the wing and in the post defensively, so hes a solid fit in my mind. The extra ~$5.5 mil the Suns lose in flexibility next summer is inconsequential right now.
Adding Melton is another a good move. Quality perimeter defender, and a guy who looks like yet another Drew Hanlen success story (one of the best shooting coaches in the world). I like Melton, although I question what he provides the Suns the next few years. Luckily, he has some shot creators next to him, plus a switchy defensive scheme, a primary ball handler, and plenty of spacing. He would have been better off in Houston, developing slowing around all that talent, but the Suns offer more minutes in a hopefully friendly environment.
Quality deal for both teams, IMO.