The main difference is that the welder uses electricity. You can put a UPS or storage battery mod on it and power it from your car, giving it infinite use with solar panels.
The Acetylene torch uses welder tanks, which are limited and non-renewable. They’re more efficient charge-wise so you can use one a lot longer than a charged welder, but once they run out they’re done. Unless you find more welder tanks, which are quite rare.