I've been told about Apium batteries which is claimed to be a 1C battery yet their infosheet (on www.apium.co.za) shows 0.5C based on the nominal charge/discharge rates. I can't find anything about it on google apart from a few dealers in PE, so I had to ask: does anybody know anything about it? Maybe it's a rebrand of something else?

Probably a rebranded battery.
From the datasheet it is a 1C battery, meaning that it will handle 1C, however their claimed lifespan is based on 0.5C, i.e. they claim 6000cycles at no more than 0.5C down to 80%DOD.  Thus using it at 1C will affect the lifespan. Pity they are not prepared to state the lifespan at 1C.
Also wonder what happens to their "guarantee" if you do use it at 1C and it should develop a fault anywhere within the 6000cycles seeing that no expected cycles are stated for that rating, so one could expect a shrug of the shoulders if something should go wrong and the BMS shows 1C usage.