Glad it went well, I'm certainly not dissing the coach, as I said I'm a fairly frequent user.
Comfort is subjective of course. IMO - More legroom, the ability to get up and walk about, quieter (Sometimes), less cramped and smelly toilets (Usually), smoother (particularly the stop start of a coach in each urban drop-off/collection point). Seats are more limited on a coach, if there's something you don't like about where you're sitting on a train there's usually an option to sit somewhere else. Even if someone considered the comfort to be equal, they're still going to be sat on the coach about twice as long as on the train. My experience is also that most of the time trains run closer to the timetable. I was five hours late into Paris on one coach, roadworks out of London, missed planned ferry, next one full, driver ran out of hours...
Maybe I was wrong to describe it as discounted, maybe I should have said you'd picked a price from the lower end of their variable pricing. I've just had a quick glance and prices seem to vary between £7 and £18, though the number of calling points and journey time are also pretty varied, far more so than you'd expect with a train. I'm now a little jealous, Flixbus don't serve Derby, National Express do, but unless I get the 3am coach it's rarely under £10.Not only that but I booked the journey myself and couldn't see any mention of it being some sort of discounted price.