This can hardly be true, given that the only onward connections from STN and LTN are with other low cost airlines...hence no connection guarantees etc. .
it is true, because the 2 sector low fares can be cheaper- I believe with some flexibility at least 50% of the time- so it is often a viable option for the traveller.
also
openjet offer travel insurance that covers missed connections, apparently most other policies do not cover this. It is a small bit more expensive a few other policies I have seen.