I'm with PatriceJ...I have never been comfortable with either knee lifts on my 6600 or 8900 but they are great machines for piecing and FMQ. I have not found the need to purchase the special bobbin case either.

I have the 8900 and love it, also have the blue dot bobbin case that I use for FMQ, I think I have less tension issues, could be my imagination. Love the knee lift.

I could not edit my post.....so here I go again....I have the 8900. Love it. It sews, quilts..free motions. The 8200 and 8900 are not embroidery ,achines, but both make beautiful 9mm wide decorative stitches. The 8900 has more decorative stitches than the 8200. PM me for dealer question. BTW the price should be dropping on these models since the 9400 is out.

And yet for me, it was the 6600 that I first used a knee lift .... and soon came to love it.
Like many things that are new, at first it did not seem right. I hated it.
Yet, I had heard so many good things about it.
So I "forced" myself to use it for a few days, when I was doing a lot of stitching.
Guess what, before long, it became 2nd nature and I definitely did not want to give it up.