There are several Rift Valley Mastacembelus species sold in the UK, such as M. ellipsifer and M. plagiostomus. Some authorities place them in the genus Caecomastacembelus, but this seems to be deprecated among fish taxonomists.
Like any other Spiny Eel they need soft sand (smooth silica sand mixed with coral sand is ideal) plus various rocks and caves for them to hide in. They are predatory and difficult to feed in a busy aquarium, so think about that before adding other Tanganyikan cichlids. Earthworms and river shrimps are popular foods, together with small pieces of seafood. As ever with strict carnivores, take care you understand about thiaminase and choose foods appropriately to minimise this problem. They feed at night, and this will be one way to get them fed without the cichlids stealing all their food, but even so, I'd get the eel settled and feeding before adding any other fish.
Other issues much like Spiny Eels generally. Sensitive to skin damage and resulting infections; jump out of aquaria given even the smallest opportunity; territorial towards one another; may be sensitive to some medications (especially copper and formalin).
Cheers, Neale