Given their company name and their listed address don't tie up on companies house I would give them a swerve

Have you looked at RRAPO or Maro?

Hi, we are almost ready to start construction on a loft and side return (planning approved, party wall done etc etc) and struggling to select a contractor. We do have a good quote from Simply Extend but a couple of things concern me 1. Very large upfront deposit 2. Outsourced model where you don’t actually know who will do the construction though they guarantee it. Has anyone got experiences with them that they’d share? Thanks!