If you mean a stick welder, yes they are good and useful, however the bigger the better and 100A is small-medium size.
However, it takes a LOT of practice to become a good welder. That means time and $$ for practice supplies. Make sure you have good safety equipment (welding helmet, gloves, etc.) and the leads from the welder are in good shape.
If you aren't inclined to spend a lot in practice, sell the unit.