Sure Vikings are great machines. I have a Husky 145 in my collection.
For that price you can always upgrade/add a better machine later.
IMO, it nice to have different machines set up for different threads and material weights.
Different machines all seem to have their own personalities. Some like to sew heavy well but suck at thin materials, and w/ others it's the opposite. I don't fight them, I just use them for what they like to do.
But don't feel like you HAVE TO BUY a particular used machine just because it might be gone if you don't. After a couple years of buying/servicing/selling used machines, the one thing I have learned is that there will ALWAYS be another good (or better) machine there next week or the week after. But like I said at $20 I don't see how you can get hurt, even if it can only do straight & zig-zag because some selector gear is broke inside.
Hunt'nFish