I'm not part of both companies, but being active on the german fractal forum, I know a bit about the history of both and how they are connected:
cabir.eu was founded after the guys shot an IR pack of a Marshall 4x12 with Greenbacks at the german Axefest, which they chose not to give away, but to sell. For this they needed a platform. The team consisted of several members, e.g.
@Morphosis and
@funkstation777 and
@tomstu. tomstu was responsible for the technical stuff, placing the mics etc. They went to the Marshall Museum and shot the IRs for the "UK Triple Collection Vol. 1 - 3". tomstu did the placement of the mics according to his technique.
However the team parted because of certain differences, which I don't know in detail and which aren't important to answer your question. After the separation cabir.eu continued and valhallir.at was founded. tomstu is now part of valhallir.at, so is funkstation777.
So when valhallir.at went to the Marshall Museum again for their "Britain's finest", they intended to shoot new IRs of the cabs used for the UK Triple Collection with a new set of mics. But they chose not to shoot them again with the mics they already used for the cabir.eu pack. So those IRs are (audibly) identical. There are differences in the post-processing, but they say it's not audible.
I guess the pricing is similar, simply because both vendors think those prices are fair. They use the same pics, I guess because they share the rights for those pics.
Is this enough information to answer your questions?
edit: I confused tomstu and oson00 ... Sorry about that