I had the CS 6000i, loved it! Fast & quiet, did very well, I don't have it anymore because a granddaughter also loved it so I gave it to her.
I used it for a backup & travel/class/Stitch Camp machine. No problems at all but I do recommend putting it on rubberized shelf lining because it is lightweight that stops it from moving around.
I also have a couple of other Brother machines from big box stores that I keep at my daughters' who live out of state, when I visit I have reliable machines to use. I also use Brother TOL's as main machines in my home, love them all.
Several years ago I wrote to Brother Co asking if machines in the discount stores & machines at dealers that were similar had any differences internally with the mechanisms-they replied in writing, that no, there is no difference.