Raymarine produces the original Autohelm in two models. The ST1000 and the ST2000. There are differences in the models. The first uses a belt the second a screw and worm system. The first is good for smaller boats and the second is great for larger boats. Although I could have used the St1000 for my 25.5, I opted for the larger weight capability. I have also been advised that my decision was good as the ST2000 is a superior mechanical instrument over the ST1000.
I enjoy the Autotiller as I do a lot of solo sailing. It gives me the freedom to move around the boat. My next upgrade is to purchase the remote so I can make changes from the front of the boat. It works with Seatalk and is NMEA2000 compatible.