I would say that Y on the BA RJ100 is pretty horrible. I have only flown Y on these aircraft in the first Y row behind club so had a club style seat. The seats are both narrow and suffer from very poor forward legroom. When you add the fact that flying time to MAD is quite long (due to the small aircraft) and the punctuality (IME) is quite poor, unless I had a good reason to fly from LCY (e.g. if like me you live very close) then I would choose to fly from elsewhere.