Well, to see the difference I´d propose you to do one thing... Do buy a pair of shears and then take these and a regular pair of scissors. Go to your tree and use both to prune some leaves or unwanted branches and them compare the two... Draw your own conclusions and then let us know your results.
But of course you can if you have one that cuts really good. Especially if the tree is young and it's not in a refinement stage. I've seen a man that practiced bonsai for 25 years without bonsai scissors and the results were amazing. The best replacement is medical equipment (sharp - stainless steel).
I agree with alainleon that perfect tools make the perfect tree but don't think you can't practice bonsai without one.
With the branch and nob cutter it's a different story.