I traded my 820 for a 770. The 770 is a bit smaller, but has embroidery (which I didn’t have with the 820). The feet work for either, but the bobbins are different. The 770 has the BSR and knee lift. And I have tons of the big cones of thread that don’t fit on the 770. So apparently I need to get a separate standing thread holder (not Bernina) so I can use those. You could check out the 570 - my friend got that for her portable machine. It has the knee lift and BSR.
sorry, I see you’ve already checked out the 570 - and I know what you’re saying about the cost of the Bernina accessories!