I have the cheapest of the Scheppachs - not sure I would buy again. It now does the job, but the bore of the wheel was not perpendicular to the face, so it took a lot of effort to get it usable. It's ok now, but I really should have sent it back.
The diamond dresser is not cheap so bear that in mind whichever make you go for.
The Scheppach is not of the same quality as the Tormek - don't know about the Jet. Then again, it is significantly cheaper. And how much will you use it? I sharpen using David Charlesworth's methodology so I only grind the primary bevel on the Scheppach, and all other work is done on waterstones.
In fact, were I to buy again, I would probably get a decent dry grinder with a decent wheel and tool guide. On the other hand, many people hone on their Tormeks as well and swear by them.
I would suggest you think carefully about whether you need one, but of you decide you do, I suggest you don't go for the Scheppach.
Dave
Dave