Disagree with ARRL handbook. Awful book. Someone really needs to rewrite all the tutorial stuff again.
All the units are in groats per dyne still.
RSGB one is useless. Mainly because it’s 80% cross references to out of date ARRL handbooks.
One problem with the older ARRL Handbooks is that they are really a compendium of QST articles, which tends to make the narrative a bit disjointed, but I think they are better than the newer ones in general.
I still think that for an Engineer from a different discipline to get a good insight into the basics, they take a lot of beating ----- surely such a person would have the Mathematical background & Googling ability to find the correct SI units, & amend the references.
(Maybe people don't have the attention span to do this, though-------I remember an Engineer many years back, who went through all the pages of "Glasford's Television Engineering" redoing all the calculations which expressly referred to the US 525 line system, & amending them for the 625 line system.)
Much of basic Electrical theory is concepts, rather than the rigid use of units, & when it gets to explanations of more advanced RF things like mixing, units haven't really changed, anyway.
I do find the use of things like 468/f to derive half wave antenna lengths in feet annoying as hell, though!
It was probably useful back in the days prior to the use of pocket calculators, but has well & truly passed its use by date!
I haven't seen a modern RSGB Manual, so it seems they may have "fallen on evil times", but the old ones were good.