omniwallet recognises maidsafecoin and is easy to send your coin from.
BUT as with ANY online wallet, you are at the mercy of the site and if you do not know the private key(s) then you cannot access your coins if the site fails/hacked/etc.
The safest place to store your maidsafecoins is in what is referred to as a “paper wallet” which is just a generated BTC address that ONLY you know the private key to. It is called a paper wallet because you make a paper copy of the public & private keys, of course you can keep a copy on say a USB too. Then you send your coins to the public address of the “paper wallet”. When you want to send the maidsafecoins from that “paper wallet” address you import the keys into say omniwallet and send them. Any remaining coins really should be sent to a new “paper wallet” for safer keeping.