If you are going to be doing some heavy bowl or spindle turning, I highly recommend the speed reducer. Turning large bowls or pedestals for tables can be an adventure at 700 rpm's. With the speed reducer, you can get down to the 100 rpm's and be more comfortable and a whole lot safer with turning those larger diameters. Been there, done that syndrome!
If you want to do some large diameter drilling in steel or even use it for those larger Forstner bits, it will come in handy for those requirements, also. It can be used in the drill press mode without using the hold down as it will slide on the rails.