I think (as in I'm sure I have read somewhere) that the Siegen Sealeys are really basic versions, with less quality control, from China, as opposed to Italy.
Have a look on
mig welding forum
Just do a search for "Siegen" on there, not very good reports in general I'm afraid.
Especially
this thread
There are usually a few 'hobby' welders for sale on there as well - like
this one
For the money, the Clarke range are pretty good value, and there is decent enough backup from them (not the chumps who work the counter at MM).
If you are only going to use it for this one project, then go ahead with the Siegen, but I plan on keeping mine for a looong time, thats why I got a portamig (British built
)