I was a little disappointed Cardano is not listed on the app.
I signed up on Robinhood as soon as I learned they were going to offer crypto trading and made a small deposit, usually my home state is last to the party it seems on everything, but i was delighted to find my invite to trade crypto on their trading platform a couple day’s ago, shockingly we did not come in last this time 
Now Robinhood needs to allow me to transfer my investment, although it seems to be a great app for trading it is not a great app for investing - I do not understand investing in something but having absolutely no way of transferring it.
Does anyone else use this app? Do you think they will add Cardano ever?
Personally I’d avoid it. See here: https://cryptoslate.com/robinhood-launches-zero-fee-crypto-trading-really-free/
TLDR: neither an exchange nor a CFD platform but a broker for other exchanges, deposits and withdrawals of crypto not possible, probable hidden charges.
If you want a legitimate platform for trading, try GDAX. It is the professional grade platform by coinbase. It also has low trading fees compared to coinbase. At least last time I checked. They don’t have ADA pairs but i wouldn’t be surprised if they added it later.
Another app worthy of mention is ABRA. They allow transfers in and out and have way more trading pairs than coinbase.
How about Circle? What do you think about it? I read an article-seems it was infomercial!
Never heard of it, sorry.