I looked at one a few years ago for a colleague who bumped into it. It's almost the same as the sequencer in the CZ5000, except the CZ5000 is 8 tracks (and it's build in the synth, which seems more useful to me). And unlike the sequencer on the RZ1, I believe you can insert and delete single notes.
The SZ1 is a 4 track sequencer, but only real-time, note recording or overdub. It can hold one song in it's memory, but it does have tape dump (which requires a din plug). It has 1 midi in and 2 out, and internal and external clock. Personally I wouldn't spend my money on it, there are much more useful sequencers around. But I reckon it can be fun to use, like the Roland jsq60 can be fun...
Edit: I found the manual on my computer: http://www.sternstudio.com/SZ1_manual.pdf