1) We-Vibe II is rechargeable, Mahana is not.
2) Mahana is waterproof, We-Vibe II is not.
3) We-Vibe II is completely made of silicone, Mahana is silicone/plastic mix.
4) Mahana is supposedly stronger.
5) Both can be used the same way, but I think the design of the We-Vibe II is better, as it's more flattened.