There are plenty of B12 products on the market, but none seem strong enough to be really useful - unless you take several as a single dose, which then makes them very expensive. All kinds of things seem to inhibit absorption, from old age to Proton Pump Inhibitors (of which I have both), which is apparently why serious cases of deficiency require injections. Research has apparently suggested that 2mg is the minimum useful oral dose - and most products seem to be 1mg or even less, some only 0.1mg, which seems to me to be totally useless.
Some products don't tell you the source of the B12; a popular source is cyanocobalamin which, as the name might indicate, is cyanide based. De-toxified, of course, but it's also much less digestible than hydroxcobalamin, which in turn seems less effective than methylcobalamin.
So I give 5 stars to this company for offering the best source of B12 at the highest strength. B12 toxicity is said to be nil, except in rare cases of allergy and a mysterious condition called Leber's, which is affected only by Cyanocobalamin.
I recommend the Pachalok/Stuart publication "Could it be B12 ?"; it's aimed at medical professionals, but covers all the issues very comprehensively.