Be careful with the notions of “true scrub plane.” To some, that means a Stanley #40. I find the #40, which I bought early on, good for edge work, but it is too narrow to be efficient on a surface- it requires too many passes. I try not to buy the kind of rough sawn that is so twisted that I’d want to take off what a #40 takes off per pass. On the other hand, I use a scrub made from an old #4 quite a bit. I have less of a camber on it (but still strong) so that I can work on rough sawn rapidly, but wider cuts per pass. Paul has a nice video here ( https://www.youtube.com/watch?v=i1r1LIkJcOg&t=7s ).
I lost track of why Paul switched from using a #4 as a scrub plane to using a #78 rebate. Can someone point me to where he discusses this? I remember a blog or video showing “hey, this can be done as an option,” but I never understood why he prefers it. It is narrower and the tote and (lack of) knob make it much less comfortable, at least for me. The 78 is about the same width as the #40 scrub, so maybe he liked the narrower width? Some of the 78 style rebate planes have a depth adjustment lever, and maybe he wanted a narrower scrub but with a depth adjuster that the #40 lacks?
Regarding the Shapton stones- I’ve freehanded on water stones, but when I do that, I know that I am risking the stone. Invariably, the edge will dig in and gouge the stone. It just happens. That cannot happen on a diamond plate (you just sort of “trip” over your sharpening, dub the edge, but don’t hurt the plate) or on an oil stone, but on a water stone, when you trip you gouge. It doesn’t stop me, but if I had a super fancy, precious water stone, like some of the Japanese natural stones, it would be heinous. Are the Shapton’s the same? Will they gouge if you stick an edge? I’ve been sharpening freehand for more than 10 years now, and this just happens now and then. The mind wanders just as the honing reaches the edge or when you are lengthening the stroke and go a bit too far.
What I mean about a true scrub plane, Is a modified #4 with a roughing/scrub blade. Who knows in the future once I have a set a 4,5,6 or 7, router, shoulder and a plow I might get a true scrub.
As far as a edge digging into the Shapton stones. Yes it can happen if your mind wonders and lose track of what your doing. Me I love sharping my steel items, I get lost in the moment while doing it. Almost like I am becoming one with the steel getting sharper more refined. Am I a master at sharping? no, I actually don’t believe there is a master in any thing as we are always learning. Once you stop learning you become complacent.