First, I should mention that I service machines - so some of the information here is about more than sewing with the 6122.
I have the 6122. It's my go to machine for most of my home sewing. It's a basic mechanical machine with IDT and utility stitches but no real decorative stitches. As others have mentioned, it's built in Germany rather than "designed in Germany" and built in China, Taiwan, etc.
It sews -almost- anything I throw at it. The only beef that I have with it is that there's no presser foot pressure adjustment and it errs on the light side so for some fabrics - usually thick seams - think the flat felled part of a pair of jeans where you turn the hem under - it may need a little help to travel over it. It's not a piercing power thing, it's a feeding thing.
Otherwise, I really don't run into any problems with it at all. It's easy to use, I find it relatively easy to service (a little harder to get into than a true vintage machine but less character building than a new plastic fantastic) and I do love the IDT.
It's a very resilient machine as well - I smashed a titanium needle on it a couple of months ago - bent it into a C shape! - and didn't throw the timing at all - the needlebar height was good as well as the hook. In the event that the timing does get thrown, the machine is well built enough that it can likely be re-timed without parts replacement. A friend hit a pin with her machine (a 7570 built around the same time) and it was simple to time.
Feet can be a bit pricey (but cheaper than say Bernina feet) so make sure that as many as possible are with the machine. The front portion of the bed swings out to make it an open arm and all of the feet and accessories are in that "flap". I would buy it again in a heartbeat - especially for $75. Around me, you rarely see them for under $250
I have no opinion on the hobbymatic. I don't have one and I haven't serviced any but all the ones I've seen do not have IDT.