Using a gauss meter placed inside the mag bodies, one can typically see an increase of around 20% on a good post-war Lucas with a blast of magnetisation, often a lot more, but they almost always work 'as is'. That using an internal magnetiser - which won't be as mega-powerful as the monster that B'macc has acquired probably! (But also not impeded by the 'air gap' of the alloy casing, because internal cores touch the poles on the inside, which helps a lot.)
It's hard to know when or whether truly full saturation has been reached - too much physics in there for me, so results are empirical. And then, the magnetism will drop off a bit and settle after the mag has been in operation.
The final result on a Lucas Alnico magnet may well be a bit stronger than on a similar-size BTH (eg KD1/KC1 or KC2 etc), but I can't measure the BTHs like-for-like from within, because the withdrawal of the armature or a keeper causes an immediate loss a great deal larger than on a Lucas (for the reasons I mentioned earlier in the thread). So external measurements like those cited are the best simple comparative guide to magnetic strength, backed up by dynamic tests to see what the magnetos actually do on test.
I can't say I have found the flip points on a typical BTH noticeably weaker than on a Lucas after a blast if things have been keepered. A well set-up K2F will deliver all sparks across three-point test gaps of 5.5mm (per Lucas spec) at around 120rpm of the armature, and so will a good BTH. (Lucas basic K series spec was I think 90% of all sparks at 130 across those gaps.) A Magdyno MO1 will do better as a rule (as the Lucas spec expects it to). But much depends on the exact 'recipe' used in a rewind and also on the air gap between armature and mag body. Some are pretty worn, after perhaps several rewinds and some truing up in lathes over the years, so their gap is larger than original and the outer extremes of their laminated parts may be smeared.
I just compared a rebuilt KC2 BTH against a rebuilt K2FC Lucas on the bench. Both delivered all sparks ahead of the Lucas spec. The flip points feel 'about the same' (with the contact breakers off to get rid of that element of friction), but without setting up a spring balance or something to measure the resistance to rotation at the flip, 'about the same' is all I can say. Plus the effect of oil seal drag and bearing grease comes into it too.
The differences in construction of the two types are also relevant to actual performance I think. The BTH (like Bosch) doesn't use a fully-laminated bobbin, relying on 4 pairs of screws to attach the end cheeks, and they are into 'solid' as they'd have to be. Lucas ones are all laminated, using through screws. Full lamination ought to reduce 'eddy currents' which impair efficiency - the sort of thing KenF loved discussing. Mechanically the BTH fixing is bullet-proof and easier to get perfect alignment after separating the armature parts. But in terms of the respective magnets, there's no doubt the K series design is better at retaining strength with the armature withdrawn, because of the extended pole pieces with reduced air gap between the ends of them in the body. Often, a K2F mag body that has stood 'empty' for years has still got a lot of magnetism in it, and the same goes for Lucas Magdynos of the same vintage.