I use FR for business trips. It serves some routes that are convenient to me and is as punctual as any other. When I go to Ayrshire, Scotland, it is more convenient to take FR to Prestwick than others to Glasgow.
But I wish those above would stop posting about low cost. I usually book on the day, or the day before. And then the fares are just what you would pay with a mainstream carrier. For example Bristol to Dublin, one-way, was a £150 walk-up fare on a 30-minute sector. OK, I was in Devon, I suddenly got the call to be in Dublin next day. And I paid it.
What I do object to, as Ryanair's High Fares passenger (and looking at their profits I suspect there are many of us) is you get the same offhand service as all others. Now I know we can't be singled out for less-rude treatment by the cabin crew (actually some of their crew bases are much better than others; well done all at PIK, unfortunately the base across the Irish Sea seems to be the one that lets the side down so often). But even when you pay those high fares, should the flight is canx due to bad weather, you just try the FR route for getting a refund of your £300 or so. Unbelievable. We haven't all paid peanuts.