Yes, they do make 2 different strengths.
(You can try and shine a bright flashlight through the bottle and see if you can read which one you have through the customs label.)
This brand uses potassium carbonate. Without the potassium levels listed, we can’t figure out the carbonate levels.
If it was me, I’d make a small test batch:
assuming 42% strength, and see how it works.
More risky would be to make 2 mini batches, one assuming 25%, and one assuming 42%, keeping in mind, that without knowing exactly what you have, the weak batch might not do much, and the strong batch may chemically burn your mouth.
I’ve found food grade carbonate on Amazon.de, so that’s what I use.