I got the LSZ-1 a little while ago, and straight out of the box I thought it was a good machine. I later added their "Monster Wheel", and realized it was a GREAT machine. Although I do use the zz (I am a noob, so no expert) I would put the Monster Wheel as a higher priority than the zz. The machine runs smoother, and deals with varying layups - and thicker layups - more easily. It made a huge difference.
As for the power, as an example, I was working on a thick layup the other day, and the needle got deflected and punched straight though this steel plate
Sumners advice on parts reflects my own. Bought and used all of those...
I would also encourage you to buy from Sailrite. (disclaimer: Just a satisfied customer). As stated, they are very friendly, helpful, and patient. I needed a bit of help to get to grips with the machine, and their manual, videos, and telephone support is unequaled.. Parts do break and get out of alignment; the Sailrite machine is easy for you to repair, tune, and get parts for. And once you start making stuff, having a supplier you can depend upon is well worth it.