I did not find using the sewing machine in itself to be a challenge, but basting the panels together and finishing the job properly certainly was. Stitching a spi on the other hand was a challenge for the sewing machine as it kept gumming up with the glue. Sailrite is usually very good on shipping their products with instructions. I expect their documentation on their sewing machines to be very good.
I expect your learning curve to be pretty steep all over, not just on the machine and seaming <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

The LSZ1 is a machine I have drooled much over, but never had the money to buy. If you intend to build several sets of dacron sails it is a good investment. Myself I like to use the modern glues as much as possible. Stitching takes time and gluing is just as good on many laminates like the Maxx series. I am certainly not going to stitch any spinnakers again except the patches and egde tapes! I would still like a LSZ1 instead of my Pfaff 1222E which is nothing more than an advanced domestic machine <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

Have a go at it, their mains and jibs are good to very good in my opinion. I would not buy beachcat spis from them as I think they have too much draft and too slack a luff.