Only Shopify requires a monthly fee, as you must subscribe to a paid ecommerce plan with ecommerce features. This includes a basic retail POS app, with an option to upgrade to the full range of POS features for $89 USD + VAT monthly.
Revolut also has a range of business account subscriptions, but they don’t give you extra features for the point of sale. If using Revolut Reader with Nobly POS, a subscription applies to that. Square and SumUp have their own advanced EPOS systems you can upgrade to at various price points.
Zettle and Square share the highest fixed rate for all cards, only marginally higher than SumUp’s. Barclaycard’s 1.6% is the lowest rate that applies to all cards. You can get a similarly low rate with Shopify, but only in conjunction with a pricey online store plan.
Elavon distinguishes between Visa and Mastercard transactions (1.75%) and other card brands (1.9% or 2.5%) which could be expensive for businesses with tourists or business clients with corporate or premium cards.
Revolut has the lowest rate dedicated to UK-issued Visa and Mastercard transactions, but the highest rate of all options for other cards, plus a small fixed fee.