My single experience was RyanAir from London Stansted to Ancona Italy. I was satisfied with the flight as I was looking for a cheap flight , to a location near Ancona, and I got a return flight for less than 100$. No extras obviously - you pay for food ( if you want it), for luggage, for being first to board etc. the flight back was canceled because of local air traffic and I was offered an alternative but needed to arrange my own transportation to the alternative site.
London Heathrow, used by regular carriers, is about as accessible as Stansted or Gatwick, so this should not affect the decision. If you want to save money and need to reach a location that is better accessed by low-cost carier- do not hesitate.