The benefits are essentially being able to add all your debit and credit cards onto the Curve card which enables you to just carry one card around with you and have access to all your cards simultaneously. You can earn cashback at a variety of retailers, some of which are always active and some of which need to be activated first. My list of retailers is mostly meh, can never see me shopping at most but there are a few decent ones tbf. I swear I was just sent my card, I don't even remember applying for it, so I'm assuming it's not much hassle to acquire. You don't have to pay for Curve but they have a paid tier too. Currently my free tier offers
Access to Fair FX
Fair exchange rates on all your cards up to €1000 per month
Fee-free Foreign ATM
Withdraw up to £200 per month
Curve Fronted
Pay your UK taxes or credit card bills with another credit card for a 1.5% fee
Smart Rules
Create unlimited Smart Rules to
automatically charge the right card as you spend
GO Back in Time
switch payments from one card to
another
All of Your Cards in One
Combine all your Mastercard and Visa cards into one single card and smart app
International Cards
Spend with your International cards with Curve for a 2.9% fee.
Fee-free Business Cards
Spend with your business funding card up to £100 per month, 1.5% fee thereafter.
You can use Samsung Pay or you can just use the cards details to make purchases online or use your physical card in stores.