Hello, I too purchased a used TWS with metal legs. Not realizing it had metal legs I went to look at the unit and make payment and planned on having a truck come the next day to pick the unit up. Because of the metal legs I was able to take the unit apart and fit it into my car and did not need to pay to have a truck pick it up. Had the legs been solid wood I would not have been able to fit the unit into my car, even with the tower removed the height of the legs would have exceeded the availability in my car to have the lift gate closed.
Of course a unit with solid wood legs is prettier than the metal legs but the funtion of the unit does not change. Check the gears, mine does not have negative gear and based on the dimensions I would prefer a unit with negative gear. This could be a cost negotiator. Basically a TWS is indestructable unless it is severly abused. I can't imagine you having any problem and all you see is wood when you're teaching.
Contact Amber at Peak Pilates to confirm but it is my understanding that any Peak Pilates reformer can be re-fitted to a TWS. It will entail the purchase of a kit which includes a new carriage (one that can flip) the tower unit with roll back bar, push through bar, light leg springs etc. (all the parts are listed on the Peak Pilates web site) and the templates where holes will need to be drilled to accomodate the poles.
Hope this helps, Happy Scooping!