Hi, sure, I have used them for 18months or so now. Yes they only accept BTC deposits, which is something I greatly prefer. I was already into crypto before hand so was no issue for me, but you need to get yourself a wallet for your BTC or other crypto. I use a Ledger, but something like Trust Wallet on your phone is fine for smaller amounts. Then buy your BTC either from an exchange like Coinbase, Binance, etc, or from and OTC desk like Instacoins (probably the simplest method as it goes straight to your wallet).
Once you have your wallet and BTC set up it’s super easy, including withdrawals. The support team is on the chat all the time too and are super helpful.