It was said to me that using a guide block to stop the chisel moving backwards would be slower but actually it has sped the process up and ensured that every joint is as close to perfect as you might want. That said though speed is never a criteria for me. I get all the speed I want at work.

I have two sets of chisèls. One I sharpen at 25 degrees and the other at 20. And if I fiddle about I can usually get excellent results with either set without the use of a guide block. But with the block I always get excellent results. It may be a case of the timber. Over the past few years I have used a lot of very soft timber where the risk of bruising the shoulders is much greater.

The other help I have found invaluable in making these joints is an alignment jig I saw on a video by David Barron

The only time I undercut is when I make half blind joints.

But back to saws which was the subject of this thread, getting a cut started in the right place is nearly essential if you want to finish in the right place. I have found that cutting a little vertically sided V shaped notch helps. I also start a cut with the saw pointed downwards a bit and on a push stroke. I have a rip saw that had a lot of set and I could make a bit of adjustment to the cut with it but it wobbled all over the place in the cut. Now the set is less I like it better.

I have a really good drop saw but it is noisy and makes a lot of mess. When my kids grew up I thought I would be done with noise and mess and so I rarely use the thing. With a nice saw and a shooting board I can get wonderful results with almost no noise or mess. I am not a talented woodworker by any means. If it is possible to make a mistake I will. But if I can cut straight without any sort of fancy guide I imagine that just about anybody can.