Most reviews discuss "effectiveness".... etc.

I posted to the quality of the maker.... whether they are labeling correctly, available to consumers for questions etc, and whether they make grandiose claims and therefore get FDA warning letters, or get closed down.

Companies with quality, and GMP practices do a pretty good job.
Jarrow is Canadian (or was but now has a US address), and I don't know if that lab site tested non US makers. But Doctor's Best, NOW, and Jarrow have always been a quality act. Country Life is also good. I don't use the pricier brands, like LEF or Thorne but they are supposed to be good too. I tested out Puritan's methyl B12 with blood work after using their new product for 3 months. It gave me very high levels.

Most raw materials come from a very few sources, so many places may get their active ingredients from the same place.
Methylfolate is one. (comes from Merck).

At one time Roche was supplying 90% of the world with vitamins they made. I don't know how that is going now, with India and China so active, but historically vitamins typically come from limited sources. So you want a packager and distributor with quality controls in place. You don't see reviews often about this aspect on iherb or Amazon.

Whether something is "effective" and "well absorbed" depends on the studies to reveal value.

So my recommendations here involve quality control, content, and cleanliness....and affordability. I spend alot of time myself selecting quality items for my home, and I share that on this board. At one time over 10 yrs ago, methylcobalamin was hard to find. We used Jarrow for several years here that I bought on iherb.com

But now I can get Puritan's and Costco's for less $$ than iherb so I have moved to those.