If you don't know your tools, then you can easily mess the knife modification and not end up with a carving knife. The chainsaw with ready made attachments is way easier to get going, but in return you have to carry the chainsaw with you and if there are any problems with the tool itself you probably aren't going to be able to fix or modify it yourself.
So it is more like trading initial speed with more precision, but also being able to do more after the initial learning curve.