I did Anderson squats for a large portion of this year regularly. Very good exercise, I'd say a few things in favour and a few things against.
1) Get's your supporting structures used to more weight at least while standing there statically.
2) Quads and lower back get worked thoroughly
1) Merely wedging yourself in and squatting up, won't give you the practice in taking weights out of the rack. I was using Anderson Squats by getting under the pins and squatting up. I used weights close to 700lbs, however I would have struggled to walk that out of the rack. So I would definitely prefer people to be walking these out and then squatting down, rather than wedging under the pins first.
2) Once again wedging yourself in and squatting up puts you in danger of strengthening the wrong groove from the bottom up. Another reason you should unrack, walkout and then Squat. Often if you can reach the bottom in a good position you can get up, but if you're messing your groove up with a poorly thought approach you will suffer.
All in all I'm in favour of them, I just think people need to use their noggins a little with the performance and how it's effecting their form on the regular Squat.