I don't think the problem is "liquid" or "more than 3 ounces".
The problem is the little icon of flames and the words "highly flammable". Flammable liquids are not allowed in checked baggage - look at any airline's website under "restricted items in baggage".
And FWIW, here's someone selling the cartridges online:
http://www.shavershop.com.au/online-store/electric-shavers/replacement-parts/braun/brau-cartrde-ccr2-refills-2pk.html who says:
PLEASE NOTE: The Braun 'Clean &Renew Cartridges' contains flammable contents, and can not be sent through the mail or to a Post Office Box.
I think if they're too dangerous to go through the mail, they'd be considered too dangerous for checked (or carry-on) baggage.