We have a branch of Leitz Tooling in Bristol, and they are brilliant.
You can spend a long time doing it yourself, and risk mucking it up, or you can get a pro to do it to "known-goodness". I do my own hand tools, obviously; I may yet attempt a bandsaw blade; but the circular blades and the knives (when thoroughly worn) go to Leitz.
I'm the proud owner of one of Mr. Maskery's honing guides, and it's brilliant for the purpoe he designed it for. But I have one set of planer knives that was "sharpened," either with a with a lump of granite off the roadside or something intended for scythes in a BBC period drama. That pair is going to Leitz, as will any of the others that gets nicked by a lump of metal.
In passing, I also have a planer knife jig for my "Tormekkalike" wet grinder, somewhere. I'm sure, in some universe somewhere, somebody has got the system to work well (for planer knives), but in my system there are just too many variables I can't easily control to get a pair of knives ground identically and well.
I don't mean honed: Steve's jig is brilliant for that. It's the complete regrind of a pair of damaged knives that's too hard to do by hand - you need the consistency of expensive machines. Given that properly ground blades transform the performance of otherwise average machines, Leitz are very good value.
E.