I have the 830 and love it. At first I wasn't getting it threaded correctly (yes, you can thread it wrong, it's hard to do, but I did) and had problems with it clacking, but when I figured out how to correctly thread it and that it likes cones of thread, it works excellent.
I use it every time I sew. I'm learning the embroidery part of it. I've had it 2 1/2 years now and am still taking lessons. My dealer is 2 hours away and I can't get over there in the winter, so I can take classes as long as I want. It does everything.
They have classes on YouTube. 21 classes. It weighs 47 pounds so I don't take it to class or retreats. I usually try not to tell people I have one because they form opinions when I tell them. I don't know why. I saved up for it.
I know that it doesn't like varigated thread to piece with (mine). But I didn't know that varigated thread was to quilt with either. I am kinda stupid sometimes. It says the thread is broken, even when it's not. Even the spools will say that the thread is broken when it's not sometimes so I bought about 10 cones of thread and haven't had one problem with it.
I have never had to change out a part on it ever. I love the knee lift, the thread cutter, how I can set it so the foot will be raised 2 mm. I love that it's self threading. I love the dual feeder the most. I buy all my feet for the dual feeder. It makes all the difference in the world to me. It has a huge manual and once in a while I look through it and find out many new things that it does and amazed by it.
I take my Viking to classes and retreats. I don't want the women at the retreats to know I own an 830 anyway. My sister owned one and they use to tease/bother her about it. I didn't like that. Neither did she. Can you believe people would actually say things to someone about their machine they own?? I would never in a million years, unless it's positive.
But, it's a very good investment, to me. I absolutely love the embroidery on it. It is so fascinating what I can do with it. It even has a cut out foot for embroidery. It's so nice!!! You can do so much with the embroidery. You can do so much on the 830. So much!!!