Buying with Coinbase is convenient but will eat a 4% of your money straight off the bat. And it does not support a deposit straight from GBP from bank account option.
Now compare to buying on Gdax (the Coinbase exchange) if one can preload Gdax with euro via a SEPA deposit ('single european payment area' integrated solution) = 0%
But how to do this? How to have a means to transform from GBP bank account to EURO and send EURO from a provisional Euro IBAN (international bank account number)
The mobile phone app Revolut means one can do this. Revolut, is free as an app, with no subscription charge. Its free to load Revolut with pound sterling. Loading the Revolut account with GDP from my card was instant.
Its 'free' to exchange from GDP to EUR (I checked the standard exchange rate- it tallies completely). This was also instant.
With the recent Revolut upgrade one can do a fee-less SEPA transfer straight into Coinbase or GDAX in Euro.
My test : I transferred 35 GDP into 39.89 EUR instantly within Revolut then used a SEPA transfer from within Revolut into Coinbase.
Revolut allows you to store the bank details of Coinbase or any other account for easy future transaction.
Coinbase/GDAX recieved my euros' into my euro wallet within 12 hours and took no fee. As long as I use a LIMIT order on Gdax my purchase of BTC/ETH/LTC was without any fee.
So theres a time factor. It it does not allow making a sudden swoop upon any flash crashes or market volatility, but it means for someone like me intending to add to their balance of BTC or ETH once a month or so, that the EUR is already sitting on Coinbase/GDAX ready to turn to BTC/ETH/LTC for such a volatility event (or just a relative dip, or just to convert and send to BITTREX), without the buyers fee.
Hope this is useful.