I'm using a Viking 630 I bought off of ebay for less than $80. I already had all the 630 attachments, plus this one came with a walking foot.
It gives me NO problems, except my darning foot broke after 4 months of use. Too impatient to wait for another, I use what they call an 'open toe' foot and it works perfectly. So, I have given up on the darning foot (which worked well too)
There's a dial I use to lower the foot pressure and one to lower the feed dogs.
I am sure I am so happy with it is because my husband built an elaborate sewing table for me. It has maybe a 7" harp and so far I've been able to fmq what I want.
Somewhere I found instructions for quilting a large quilt in sections and I do use that. Like I said, the table, with its support, is probably why it all works.