By no means an exhaustive test, but I've been unhappy with the results of using the honing guide and my diamond plates (Fine, Extra fine and Extra Extra fine), getting the smooth operation into the Maple I often work with. (sorry for the grammar).
I recently got a Tilt box after seeing interesting discrepancies in a picture on Derek Cohen's <www.inthewoodshop.com>, decided to do my own tests. The results were similar, of course; when I set the guide for 25 deg, the plane blade had a marked space under it, on the plate; if I set the primary bevel on the plate so it were flat, it was about 23 1/2 deg. It meant that I was supposedly working very hard to get an iron which had a different angle than indicated on the box, to fit a suggested hone angle on the guide.
I HAVE NOT, tried to play with the various combinations of angles on both the holder and the projecting guide; even though i'm "almost retired(!)" my time has value. That will come next week.
I spoke with Customer Service at LV, who set me straight. The 25 deg. iron isn't 25 deg, it's about 23.5 deg, and the SECONDARY bevel should be 25 deg. They may mention that in the little paper that comes with the irons, but as a typical male, who reads the instructions LOL! Same factors with the 38 and 50 deg. irons.
What I did as a short cut, was to eliminate the guide, and honed up the blades using the bevel built in by LV; place the bevel flat on the plate, tighten the holder, check for perpendicular using my sliding gauge, and going through the plates firstly at the primary bevel, then adding the secondary one.
As said I'm working with end grain Maple, so I used my 50 deg. iron in the LAS to joint an edge.
Using this system, the plane just sang! Almost zero tear-out and cut sweet.
I'll enjoy the experimenting, but as a long time contractor, this is a whole new ball game for me.
I do have a number of newer and older Stanleys that I sharpen and bevel accurately on the Mk II, but it seems the BU irons are different.
Learning new things is fun.