LetBuddy is landlord software built and run in the UK, for one property or several hundred. Each property holds its certificates (gas, EICR, EPC and the rest) with the legal renewal period built in and reminders before and after they lapse; a dated rent ledger, with bank statements imported and matched rather than retyped; tenancy records with deposit deadlines by nation and a paper trail that stands up under Section 8; and income and expenses in HMRC's own categories, with Making Tax Digital quarter reminders. Users are unlimited, and each can be limited to the properties you choose.
The first property is free with every feature and no card, permanently. Beyond that, one rate per property that falls as the portfolio grows and stops at £50 a month. Nothing is gated and nothing carries a surcharge, and the rate you sign up at is the rate you keep.