I have the modern/computerized 820. My machine is a bit fussy and has earned the name "Cranky Bernie". Bernie is really fussy with threads,I'm its 3rd owner, it has always been well maintained and cleaned and all that. I repaired/replaced the Thread Sensor unit in 2020, and then again a year later in 2021, and then the replacement part failed within about 2 weeks and broke and I had it replaced again (that third time was fully under warranty, no cost for parts or labor).
I'm starting to get a lot of error messages again... Don't want to jinx myself but I really want to get through this project.
Turns out that I really like the thread cutter and I would be disappointed if it didn't work for me.
There are many things I love about this machine when it works. The previous two owners kept with Bernina and are very happy with their replacement choices (a 660 and 720 if I recall). I'm not so tied to the brand loyalty and am considering other options over repairing (again and again).