I'm going to have a 22 hours layover but I decided to stick with the Ren at LHR. I got it LNFed down to less than GBP 50, which is around 1/3 of what the hotels cost inside London. Taking the tube is no big deal - as long as you don't do it during rush hours and fortunately my layover is during a weekend so my quick trip into London with 3 small kids should be doable.

I saw that the lounge is closed during weekends - that's the main drawback. Can't see anywhere about if the breakfast is going to be in the lounge.